2026 Forest River Sandpiper 3990FL vs 4003MB
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Key differences
Both are 2026 Fifth wheel models from the Forest River Sandpiper line. Here's how they differ, from manufacturer specifications.
- The 3990FL is 9″ longer: 43′ 6″ vs 42′ 9″.
- The 3990FL is 170 lb lighter unloaded: 12,439 vs 12,609 lb.
- The 4003MB has a 125 lb higher GVWR: 15,500 vs 15,375 lb.
- The 3990FL lists 45 lb more cargo capacity: 2,936 vs 2,891 lb.
- The 4003MB has a 815 lb lighter hitch weight: 2,010 vs 2,825 lb.
- The 3990FL has 5 slide-outs; the 4003MB has 4.
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YOUR SHORTLIST
Floorplan
PRICING
Manufacturer price (USD)
Not verified
Not verified
Lowest tracked dealer price (USD)
No recently verified dealer price
No recently verified dealer price
Est. monthly payment (USD)
No verified price to estimate from
No verified price to estimate from
DIMENSIONS & WEIGHTS
Exterior length
43′ 6″
42′ 9″
Exterior width
8′ 0″
8′ 0″
Exterior height
13′ 4″
13′ 4″
Shipping / unloaded weight
12,439 lb
12,609 lb
GVWR
15,375 lb
15,500 lb
Listed cargo capacity
2,936 lb
2,891 lb
Listed hitch weight
2,825 lb
2,010 lb
LIVING & SLEEPING
Sleeping capacity
—
—
Slide-outs
5
4
Main bed
Not verified
Not verified
Bunk beds
Not verified
✓ Yes
Dinette
Not verified
Not verified
Bathroom
Not verified
Not verified
Refrigerator
Not verified
Not verified
TANKS & EVERYDAY FEATURES
Fresh water
50 gal
50 gal
Gray water
80 gal
100 gal
Black water
50 gal
50 gal
Awning length
21′ 0″
10′ 8″ & 20′ 0″
Shore power / electrical service
Not verified
Not verified
Solar equipment
Not verified
Not verified
Outdoor kitchen
Not verified
✓ Yes
Washer/dryer prep
Not verified
Not verified
Microwave
Not verified
Not verified
Cooktop
Not verified
Not verified
Air conditioning
Not verified
Not verified
Electric fireplace
Not verified
Not verified
Backup camera
Not verified
Not verified
Propane tanks
—
—
Tire size
Not verified
Not verified
SOURCES & VERIFICATION
Weight basis
Manufacturer unloaded vehicle weight
Manufacturer unloaded vehicle weight
Source checked
2026-10-28 Manufacturer ↗
2026-10-28 Manufacturer ↗
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Manufacturer floorplan images © their respective manufacturers. Specs checked October 19, 2026; exact-unit labels and production options may differ. “Not verified” or a dash means we have no confirmed value. “Not listed” means the applicable manufacturer equipment was checked but does not mention the feature; it does not mean “No.” “Conflicting data” means manufacturer entries disagree. “Optional” equipment is available but is not confirmed as standard. Camera prep does not confirm an installed camera. Weights are kept separate: unloaded weight, GVWR, cargo capacity, and hitch weight. Confirm every specification for the exact model year and configuration with the manufacturer. This tool does not establish towing compatibility.
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