New 2026 Grand Design Momentum 399M
Colton, CAMike Thompson's RV
Questions about this 2026 Grand Design Momentum 399M
What does it cost?
Mike Thompson's RV lists it at $129,998.
Is it new or used?
New. It is a 2026 model.
Is it still for sale?
Mike Thompson's RV’s website listed it for sale on October 31, 2026. RV Shift checks dealers’ websites about once a day, so ask the dealer to be sure.
Where is it?
At Mike Thompson's RV in Colton, CA. See all 38 RVs Mike Thompson's RV lists on RV Shift.
How many people does it sleep?
The dealer lists it as sleeping 4.
How long is it?
44' 10", with 3 slide-outs, as the dealer lists it.
How much does it weigh?
The dealer lists a dry weight (empty) of 18,000 lb, a GVWR (the most it is allowed to weigh loaded) of 22,500 lb and a hitch weight of 3,464 lb.
What does it take to tow it?
RV Finder’s estimate: it needs a vehicle rated to tow about 19,200 lb, with a fifth-wheel hitch. That is its 18,000 lb dry weight plus 1,200 lb for water and gear, rounded up to the next 100 lb. The listing doesn’t say whether it’s a fifth wheel or a bumper-pull. RV Finder judged it as a fifth wheel from its weights: ask the dealer. RV Finder shows whether it is within your vehicle’s published rating, from the maker’s own towing guide, and checks tongue weight and payload too. Confirm your numbers in your owner’s manual and on the sticker in the driver’s door jamb. Check it in RV Finder
How do I ask the dealer about it?
Use the Check availability form on this page. Your message comes to RV Shift and we pass it to Mike Thompson's RV.
About this RV
Grand Design Momentum fifth wheel toy hauler 399M highlights: • Front Private Bedroom • Kitchen Island • Hybrid Desk/Dinette • Unobstructed Pass-Thru Storage • Side Patio This toy hauler has all the comfort and convenience you could ask for! Once you have unloaded your toys from the 12' 6" separate garage, you can start lunch on the exterior griddle located by the side patio. There is also a 65" TV here and a 1.7 cu. ft. refrigerator to entertain guests! And if you have guests staying over, you can choose to add the optional Liftsuite system with underside can lights in the garage. If the weather isn't cooperating, you can make meals in the fully equipped interior kitchen, complete with an island, pantry, pull-out countertop extension and more. An L-shaped sofa with recliners is in perfect view of the 50" TV and fireplace, and there is even a hybrid desk/dinette with windows where you can get some work done if needed. Head towards the front to freshen up in the full bath before heading to bed in the private bedroom.
Specifications as listed by the dealer
- Type
- Toy hauler
- Condition
- New
- Year
- 2026
- Make
- Grand Design
- Model
- Momentum 399M
- Stock number
- MN26026
- VIN
- 573FM4739TBB04657
- Sleeps
- 4
- Slides
- 3
- Length
- 44 ft 10 in
- Ext Width
- 8 ft 5 in
- Ext Height
- 13 ft 6 in
- Int Height
- 8 ft 5 in
- Interior Color
- SLATE- STANDARD WOOD
- Exterior Color
- STANDARD PAINT
- Hitch Weight
- 3,464 lbs
- GVWR
- 22,500 lbs
- Dry Weight
- 18,000 lbs
- Fresh Water Capacity
- 140 gals
- Grey Water Capacity
- 104 gals
- Black Water Capacity
- 52 gals
- Tire Size
- 17.5"
- Furnace BTU
- 35,000 btu
- Fuel Capacity
- 60 gals
- Available Beds
- Queen
- Refrigerator Type
- 12V Stainless Steel
- Refrigerator Size
- 20 cu ft
- Cooktop Burners
- 3
- Number of Awnings
- 3
- Axle Weight
- 7,000 lbs
- Garage Size
- 12 ft 6 in
- LP Tank Capacity
- 30 lbs
- Water Heater Type
- On Demand
- AC BTU
- 30,000 btu
- TV Info
- LR 50" LED TV, Garage 32" LED TV, Patio 65" TV
- Awning Info
- 9', 12', 14' Power w/LED Lights
- Axle Count
- 3
- Washer/Dryer Available
- Yes
- Number of LP Tanks
- 2
- Shower Type
- Shower w/Seat
- Electrical Service
- 50 amp
Features
- Keyed Alike™ Ramp Door Latches
- 2nd Patio Awning w/ LED Lights
- 3rd Awning w/ LED Lights
- Exterior Color Changing LED Accent Lighting
- High-Gloss Gel Coat Exterior Sidewalls
- Door Side Exterior Spray Port
- Frameless Tinted Windows
- Walk-On Roof
- 17.5" Spare Tire (Undermount)
- MORryde Strut Assist Entry Step
- Slam-Latch Baggage Doors
- Mo Secure
- Gen III 3 Seasons Doors (Opt)
- 101" Wide Body Construction
- 5-Side Aluminum Cage Construction
- Fully Enclosed and Heated, Underbelly and Storage Area
- Upgraded Axle Hangers
- Heavy Duty H-Rated Tires
- Heavy Duty 7,000 lb. Axles with ABS Brakes
- 17.5" H-Rated Aluminum Wheels
- MORryde® Independent Suspension 2.0
- 6-Point Hydraulic Leveling System
- MORryde® Pin Box
- 101" Wide Body Super Chassis w/Drop-Frame Storage
- Interior Color Changing LED Accent Lighting
- Hardwood Cabinet Doors w/Hidden Hinges
- Recliner Sofa w/Adjustable Headrest or Flip Down Cupholders
- Central Vacuum System w/ Tools and Dust Pan
- Plywood Drawer Bottoms
- Microwave
- Professional Grade Stainless Steel Cooktop
- 12-Volt High Power MaxxAir w/Rain Sensor
- Window Behind Range
- Kitchen Barstools w/ Extended Countertops
- Smart Sink w/Removable Cutting Board, Produce Strainer and Glass Rinser
- Solar Prep (10-gauge wiring with universal MC4 connectors)
- 75 Amp Converter
- 12V Battery Disconnect
- 12V High Power Fan (Kitchen)
- 35k BTU High-Capacity Furnace
Listing and photos: Mike Thompson's RV. Details come from the dealership and can change; confirm them before you buy.