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Forest River Sierra 4003MB

Fifth wheelbuilt 2023– (in production)Mixed build tierCommon on the used market
WHAT ONE COSTS
$97,400est. MSRP (from 26 priced floorplans of this line)

Still in production. A used 2023 would run roughly $57,500.

WHAT IT WEIGHS BEHIND YOUR TRUCK
~13,826 lbestimated as towed, for 2 people

dry weight 12,609 lb + fresh water (50 gal, full) 417 lb + propane + battery 200 lb + gear for 2 600 lb. Brochure dry weight omits water, propane, batteries and your gear; this estimate doesn't.

You want a tow rating around15,365 lb (10% margin)
GVWR (the sticker maximum)15,500 lb
Tongue weight, loaded~2,204 lb (16%)
Cargo capacity2,891 lb
WHICH TOW VEHICLES IT FITS: 19 OF 95

Judged the way the app judges: estimated loaded weight against each vehicle's rating less a 10% margin, per model year, because the 4003MB's published weights held steady. Fifth wheels also need a pickup bed and are held to the fifth-wheel rating where published.

VEHICLETOW RATINGVERDICT
Chevrolet Silverado / GMC Sierra 2500HD (Duramax, max tow) '24-2622,500 lbfits, loaded, with 10% margin
Chevrolet Silverado / GMC Sierra 2500HD (Duramax) '20-2318,510 lbfits, loaded, with 10% margin
Chevrolet Silverado / GMC Sierra 2500HD (Duramax) '11-1918,100 lbfits, loaded, with 10% margin
Chevrolet Silverado / GMC Sierra 3500HD (Duramax DRW, gooseneck) '20-2636,000 lbfits, loaded, with 10% margin
Chevrolet Silverado / GMC Sierra 3500HD (Duramax DRW, gooseneck) '11-1923,300 lbfits, loaded, with 10% margin
Ford F-250 Super Duty (6.7 diesel, gooseneck) '20-2222,800 lbfits, loaded, with 10% margin
Ford F-250 Super Duty (6.7 diesel, tow pkg) '17-1918,000 lbfits, loaded, with 10% margin
Ford F-250 Super Duty (6.7 diesel) '11-1616,600 lbfits, loaded, with 10% margin
Ford F-250 Super Duty (6.7 HO diesel, gooseneck) '23-2623,000 lbfits, loaded, with 10% margin
Ford F-350 Super Duty (6.7 diesel DRW, gooseneck) '17-1932,500 lbfits, loaded, with 10% margin
Ford F-350 Super Duty (6.7 diesel DRW, gooseneck) '20-2237,000 lbfits, loaded, with 10% margin
Ford F-350 Super Duty (6.7 diesel DRW, gooseneck) '11-1621,600 lbfits, loaded, with 10% margin
Ford F-350 Super Duty (6.7 HO diesel DRW, gooseneck) '23-2638,000 lbfits, loaded, with 10% margin
Ford F-450 Super Duty (6.7 HO diesel DRW, gooseneck) '23-2640,000 lbfits, loaded, with 10% margin
Ram 2500 (6.7 Cummins HO) '19-2620,000 lbfits, loaded, with 10% margin
Ram 2500 (6.7 Cummins) '11-1817,980 lbfits, loaded, with 10% margin
Ram 3500 (6.7 Cummins DRW, gooseneck) '13-1831,210 lbfits, loaded, with 10% margin
Ram 3500 (6.7 Cummins HO DRW, gooseneck) '25-2636,610 lbfits, loaded, with 10% margin
Ram 3500 (6.7 Cummins HO DRW, gooseneck) '19-2437,090 lbfits, loaded, with 10% margin
The 76it doesn't fit

These verdicts assume 2 people aboard with typical gear. See the margin for your truck and your crew →

THE SPECS
Length42.8 ft
Height (incl. A/C)13.3 ft
Width8.0 ft
GVWR15,500 lb
Dry weight12,609 lb
Dry tongue weight2,010 lb
Cargo capacity2,891 lb
Sleeps7
Slide-outs4
Axles2
Fresh water50 gal
Grey water100 gal
Black water50 gal
Air conditioning15,000 BTU

A missing row means the maker never published that figure: unknown, not zero.

WHERE PEOPLE SLEEP
  • 1× Front RV king bed(Permanent)72×80
  • 1× Double bunk(Permanent)54×74
  • 1× Bunk(Permanent)—
  • 2× Dinette and sofas convert to beds(Convertible)—
HOW IT'S BUILT: 4/5
WallsLaminated fiberglass
FrameAluminum
RoofWalk-on
UnderbellyEnclosed

Forest River (Mixed tier): Sierra is the Sandpiper's badge twin - welded aluminum-framed laminated construction, mid-pack Forest River quality control.

YEAR BY YEAR: WHAT CHANGED
  • 2023Introduced
FINDING ONE

Common: usually several for sale within a day’s drive. Why: Forest River is a volume manufacturer; still in production. Estimated from build volume and production span, not a count of live listings.

OUR TAKE

Mid-bunk plan with a surprisingly light 2,010 lb pin for a 42-footer.

OTHER SIERRA FLOORPLANS
2850RL · 10,000 lb · sleeps 6321RL · 13,669 lb · sleeps 43250IK · 10,000 lb · sleeps 63330BH · 13,769 lb · sleeps 63370RLS · 13,560 lb · sleeps 43440BH · 14,075 lb · sleeps 63550BH · 15,500 lb · sleeps 83660MB · 14,115 lb · sleeps 6368FBDS · 15,500 lb · sleeps 63710HBFB · 15,500 lb · sleeps 8372LOK · 15,500 lb · sleeps 8373BH · 15,500 lb · sleeps 63770FL · 14,175 lb · sleeps 6377FLIK · 15,500 lb · sleeps 8the whole line →
Find one for sale

Live listings for the 4003MB on the big marketplaces. Each search opens pre-filled with this exact floorplan:

RV Trader ↗Camping World ↗FB Marketplace ↗Google ↗

Inventory varies by site and day. Slim pickings? search the whole Sierra line ↗

Is the 4003MB your #1, or just a spec sheet?

These are the facts. Whether it beats the other six thousand rigs for you depends on what you care about. Set your priorities as sliders, switch on your hard limits, and watch the whole market re-rank around them. Every exclusion explained, every margin shown.

See where it ranks for you →

Data compiled from dealer and aggregator listings, retrieved 2026-07.