01 What makes it unique
The 388MBS is the Solitude built for families who want a separate place to put the kids. Its defining feature is a middle bunkroom — a dedicated bunk zone amidships, between the front master suite and the rear living area — rather than a second full bath. The back of the coach holds a rear living area with rear entertainment, and the whole plan sits under a lower 12-foot-9 roof on four slide-outs, a half foot shorter than the 13-foot-5 standard plans for easier garage and overpass clearance.
It is one of the heavier standard plans at a 15,985-pound dry weight, reflecting the bunkroom and the longer 43-foot body, which leaves a 3,015-pound payload and a 2,930-pound dry pin. RVUSA lists a published 19,000-pound GVWR on the standard Solitude build — the 101-inch widebody drop-frame chassis, a MORryde pin box, a heated underbelly, 330-watt roof solar and a 20-cubic-foot 12-volt refrigerator — with a single 15,000-BTU air conditioner standard. A 53-gallon black tank serves the single bath.
At an MSRP of $163,220 it sits among the upper plans. For a family that wants a dedicated bunkroom rather than the two-full-bath 391DL’s second bathroom — and a lower roof line — the middle-bunkroom 388MBS is the family Solitude on the standard 19,000-pound chassis.
02 Full specifications
Dimensions
- Exterior length
- 42' 11"
- Exterior width
- 8' 5"
- Exterior height
- 12' 9"
- Interior height
- 8' 0"
Weights
- Dry / unit base weight
- 15,985 lbs
- GVWR (max loaded)
- 19,000 lbs
- Net cargo / payload
- 3,015 lbs
- Dry pin weight
- 2,930 lbs
Capacities
- Fresh water
- 81 gal
- Grey water
- 106 gal
- Black water
- 53 gal
- Refrigerator
- 20 cu ft
Construction
- Frame
- Drop-frame · 101" widebody
- Walls
- 5-side aluminum cage · laminated
- Roof
- Walk-on TPO · limited-lifetime warranty
- Underbelly
- Fully enclosed · heated tanks & storage
Running gear
- Axles
- 2 (8,000 lb tandem)
- Hitch
- Fifth-wheel (in-bed) · MORryde® pin box
- Suspension
- MORryde® CRE3000 · Tow Assist ABS
- Tires
- 17.5" H-rated Cooper
Galley & bath
- Cooktop
- Professional-grade SS · built-in oven
- Refrigerator
- 20 cu ft
- A/C
- 15,000 BTU (single)
- Water heater
- On-demand · whole-house filtration
Sleeping & layout
- Sleeps
- 5
- Slides
- 4
- Awnings
- 2
- Primary bed
- King
Verified specs, drawn to scale
Original graphics built from this floorplan’s own verified figures.
Loaded weight budget
Size, drawn to scale
Holding tanks
Drawn by this site from the verified figures above, never traced from a manufacturer drawing; a graphic is left out where its figure is not published. Full record: dataset.
What it takes to tow this
Built from this floorplan’s verified weights. We publish the trailer side only.
Truck tow ratings are not listed: one model varies by thousands of pounds across engine, axle ratio, cab and package. The loaded range is the 15–25% pin-weight convention for fifth wheels, applied to this plan’s 19,000 lb GVWR, not a measurement of this unit. Hitch class is not used as a rating (SAE J684 covers trailers to 10,000 lb GVWR); read the rating stamped on your hitch. On this plan the convention band’s low end fell below the published dry figure, so the range starts at the published dry weight instead — loaded is never lighter than dry.
03 The Solitude floorplan family
Solitude is Grand Design's flagship fifth wheel and one of the best-selling luxury extended-stay fifth wheels in North America. The line runs to ten floorplans for 2026; the eight highest-demand layouts are profiled here in full, and the remaining two are catalogued on the line hub. The 388MBS on this page is highlighted; each other profiled plan links to its own page.
| Floorplan | Nominal | Sleeps | Notable |
|---|---|---|---|
| 310GK | 34 ft | 4 | Light rear-kitchen entry, sub-13k dry |
| 370DV | 38 ft | 4 | Rear living, central island + prep bar |
| 380FL | 41 ft | 6 | Front living, bath-and-a-half, 5 slides |
| 382WB | 41 ft | 6 | Separate front living room, 5 slides |
| 376RD | 42 ft | 6 | Raised rear den, three sofas |
| 390RK | 42 ft | 6 | Rear kitchen, outdoor kitchen, 5 slides |
| 391DL | 42 ft | 8 | Two full baths, dual entry, sleeps 8 |
| 388MBS | 43 ft | 5 | Middle bunkroom, family, lower profile |
| 417KB | 42 ft | 4 | Rear kitchen, bath-and-a-half, master |
| 414LJMJ | 43 ft | 6 | Triple-axle flagship, mid bunk + loft |
Solitude is Grand Design's flagship extended-stay fifth wheel and one of the best-selling luxury fifth wheels in North America. The full line runs to ten floorplans for 2026; eight are profiled here and two more are catalogued above. Every plan rides on the same drop-frame 101-inch widebody chassis with a MORryde pin box, 8,000-pound axles and a fully enclosed heated underbelly, and ships with a 330-watt roof solar package, a 20-cubic-foot 12-volt refrigerator and an on-demand water heater with whole-house filtration as standard. Body specifications (lengths, heights, payload, tanks, sleeping, slides and awnings) are RVUSA-verified against the 2026 structured spec records, each page fp-slug and title checked; dry weight, GVWR, payload and pin weight are published per plan, and each plan's dry weight plus payload equals its GVWR exactly. Real loaded pin weights run higher — always weigh the loaded coach and confirm against your truck's payload and rear-axle ratings.
04 Notes on this floorplan
Middle bunkroom
A dedicated bunk zone amidships between the master suite and the rear living area — a separate place for kids or guests.
Lower 12-foot-9 roof
A half foot shorter than the standard 13-foot-5 plans — easier garage, overpass and storage clearance.
Rear living + entertainment
A rear living area with rear entertainment behind the bunkroom — a family layout that keeps the main lounge at the back.
Heavier standard plan
At 15,985 lb dry with a 3,015-lb payload, it is one of the heavier 19,000-lb plans; confirm a properly rated 3/4- or 1-ton truck.
05 How it compares
The two-full-bath family plan — a full second bathroom and sleeps eight instead of a middle bunkroom.
The triple-axle flagship — a bunk-and-loft on a heavier 23,500-lb chassis with the largest tanks in the line.
Keystone’s middle-bunkroom-and-loft plan — the direct big-luxury-FW cross-shop.
06 Loading it for a trip
This floorplan carries its water comfortably. A full 81-gallon fresh tank is roughly 22% of the 3,015-pound cargo capacity, leaving the 388MBS with a usable gear budget even when you tow full.
| Weight budget | Figure | What it means |
|---|---|---|
| Cargo capacity as published (CCC) | 3,015 lb | Everything you add: gear, water, propane, batteries, food, people’s belongings. |
| Fresh tank filled (81 gal × 8.34 lb) | −676 lb | Water is the heaviest thing most owners add, and it is added first. |
| Cargo budget left with a full fresh tank | 2,339 lb | 22% of this plan’s capacity is spent before a single bag is loaded. |
| Per sleeping position, water aboard | 468 lb | A rough share of what is left across the 5 berths this plan sleeps. |
The published dry pin weight of 2,930 pounds is 18% of this floorplan’s 15,985-pound dry weight. Fifth-wheel pin weight rides in the bed of the truck, so it comes off payload rather than off tow rating — and it rises with the trailer as you load it, not in proportion to what you put over the axles.
Nothing above changes the ceiling. Loaded to its 19,000-pound GVWR the 388MBS is towing 3,015 pounds more than its 15,985-pound dry figure, and that is the number your vehicle has to be rated for — not the brochure weight.
Tank balance is generous here: 81 gallons of fresh against 106 grey and 53 black, so waste capacity keeps pace with supply and the fresh tank is the constraint that ends a dry stay.
07 Where this floorplan sits
Ranked by GVWR, the 388MBS sits 6 of 10 in the Solitude line: 19,000 pounds against a line that runs from 19,000 to 23,500 pounds. That position is the useful thing to know, because the plans immediately either side of it are the real alternatives.
Either side of it in the same line: Solitude 382WB matches it exactly at 19,000 lb GVWR; and Solitude 390RK matches it exactly at 19,000 lb GVWR.
8 other Solitude plans share this floorplan’s 19,000 lb GVWR, so the ranking above separates plans that tow to the same ceiling. On a shared chassis the figure that actually differs between them is cargo capacity and where the weight sits, not the rating.
| Comparable fifth wheels | GVWR (lb) | Dry (lb) | Sleeps | Length |
|---|---|---|---|---|
| 388MBS | 19,000 | 15,985 | 5 | 42 ft 11 in |
| Influence 3804DS | 19,000 | 14,603 | 6 | 42 ft 6 in |
| Momentum 344M | 19,000 | 15,910 | 6 | 39 ft 11 in |
| Paradigm 385FL | 19,000 | 15,487 | 6 | 41 ft 4 in |
| Seismic 3512 | 18,995 | 14,285 | 7 | 41 ft 7 in |
| Riverstone 39RKFB | 18,975 | 16,511 | 4 | 42 ft 1 in |
| Bighorn 40DB | 18,850 | 16,110 | 8 | 43 ft 10 in |
Against the 388MBS: the Influence 3804DS sleeps 1 more; the Momentum 344M is 3 ft shorter and sleeps 1 more; the Paradigm 385FL is 2 ft shorter and sleeps 1 more. Those are differences in the published numbers only — what they cost, how they are built and how they live are separate questions each of those pages answers on its own terms.
Those are the nearest fifth wheels from other lines by weight — one per line, picked by proximity on that figure and nothing else. They are listed so the same tow vehicle can be checked against real alternatives, not because they are equivalent inside; layout, build and price diverge sharply across that group.
For scale, the Solitude floorplans profiled here run 12,100 to 19,000 pounds dry and 34 to 43 feet of exterior length across 10 plans. Where a floorplan falls in that spread usually says more about which vehicle can tow it, and which site it fits, than the layout name does.
Every profiled floorplan in this line, with the full weight table, is on the Solitude line hub.
08 Common questions about the 388MBS
How much does the 388MBS weigh?
Its published dry weight is 15,985 lb and its GVWR is 19,000 lb, so 3,015 lb separates the empty trailer from its rated maximum. By GVWR it is the 5th-heaviest of the 10 Solitude floorplans profiled here that publish a GVWR (19,000 lb to 23,500 lb). Size the tow vehicle to the 19,000 lb figure, not the dry one.
How much can the 388MBS carry?
Cargo carrying capacity is 3,015 lb, 16% of the GVWR. Across the 307 fifth wheels on this site that publish both figures, the median share is 19%, so this plan sits 3 points below the median. A full 81-gallon fresh tank is about 676 lb of it (22%), because federal rule counts on-board water as cargo (49 CFR 571.120 S10.4.2). The yellow cargo-capacity label inside your own trailer’s entry door (49 CFR 571.120 S10.4.3) states the figure for that unit as delivered, options included, and it is the one that binds.
What is the pin weight of the 388MBS?
The published dry pin weight is 2,930 lb, 18% of the dry weight. Across the 386 fifth wheels on this site that publish both figures, the median dry pin share is 19%, so this plan sits close to the median. Loaded, it changes with where the cargo sits, and it is carried by the tow vehicle’s payload, not its tow rating.
What size tow vehicle does the 388MBS need?
A tow rating of at least 19,000 lb, this floorplan’s GVWR, plus enough payload for the pin load, passengers and cargo. The dry pin weight alone takes 2,930 lb of that payload before anything is loaded. Payload is printed on the tire and loading placard on the tow vehicle’s driver-side door pillar (49 CFR 571.110 S4.3); this site lists no truck ratings because they vary by build.
How many people does the 388MBS sleep?
It is rated to sleep 5. 6 of the 10 Solitude floorplans profiled here that publish a count are rated for more. Rated positions include convertible furniture.
What are the tank capacities on the 388MBS?
Fresh 81 gallons, grey 106 gallons, black 53 gallons. The smallest of the three is the black tank, at 53 gallons. Combined waste capacity is 159 gallons.
How long is the 388MBS?
Exterior length is 42' 11". That makes it the longest of the 10 Solitude floorplans profiled here that publish an exterior length (34 ft 4 in to 42 ft 11 in). Check it against campsite and storage length; the exterior figure includes the tongue or pin box.
Every figure in these answers is read from this page’s verified specification table. Where the manufacturer publishes nothing, the question is not answered rather than estimated.
09 What this page publishes, and what it does not
Named sources publish 18 of the 18 specification fields this catalogue tracks for the 388MBS (98% complete on the full field set).
Not published for this floorplan: tire size (a tire description is published, a size is not). Those rows are left blank rather than copied from a sibling floorplan.
Sourcing rules: methodology.
11 NHTSA safety record
This floorplan belongs to the Solitude line, and NHTSA holds 15 recall campaigns and 135 owner complaints against that line. They are separate records and are not added together — a recall is a manufacturer-confirmed defect with a remedy; a complaint is one owner’s account, which NHTSA does not verify.
What to look at on a used one. Across the 135 complaints filed on this line the most-reported components are structure (30%), unknown or other (19%) and service brakes (14%). That is where owners of this family have had trouble, so it is where an inspection is worth the time.
Recall coverage is not complete — our harvest of NHTSA’s recall API ran 1,556 queries, of which 0 failed and 242 returned an explicit zero. A line can still be under-reported where NHTSA files a roster under a parent name, or where a match rests on the wording of the recall rather than its model field. Complaints come from the complete bulk file but are unverified and self-selected: a high count tracks how many units a line sold at least as much as how well it was built. Check a specific VIN at NHTSA before you buy. Full tables are on the Solitude line page.