Used 2018 Grand Design RV Momentum 399th for sale at Blue Fox RV in North Logan, UT. Sleeps 9, 43.3 ft long, 3 slides. Listed at $64,995.

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Used On the lot

2018 Grand Design RV Momentum 399th

Stock #206357 North Logan, UT
$64,995
Est. Monthly
$467/mo
$12,999 down · 6.99% APR · 180 mo
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Length
43 ft
Sleeps
9 ppl
Slideouts
3
GVWR
20,000 lbs
Dry Weight
15,900 lbs

Built for the road, ready for your next trip.

You can pack a whole lot of fun into this Momentum toy hauler fifth wheel by Grand Design!  Model 399TH offers a 13' garage for the toys, plenty of sleeping space for a few extra buddies to tag along, and kitchen and bath amenities like home. Check it out....one and a half baths, a fireplace, an 18 cu. ft. refrigerator, and a fold down side patio, plus so much more!  How's that for living on the edge....of fun that is!

With 13' of toy parking space you can take it all.  The rear ramp door will make loading and unloading a snap.  You can even choose a rear ramp door patio option as well. Inside the garage area you will find an LED TV, overhead cabinets in the corner, an overhead loft near the front of the garage, and a half bath so you can easily keep all the dirt and grim out of the main living space.  You can even add an optional Happi-Jac with rollover sofas including a top bed for added seating and sleeping space once the toys are removed. In the cargo area there is a side man entry door for quick access to the garage and half bath, a location that has been prepped for a washer and dryer.

Head into the main living area to find a sliding glass door to a fold-down side patio to enjoy a little down time outdoors along the curb sideOn the inside of this cool toy hauler you will find a home like space filled with everything you need to relax and refuel for another day of fun.  There are dual opposing slides in the main living room and kitchen area.  An 18 cu. ft. refrigerator will keep all of your cold stuff cold, and there is a three burner range and overhead microwave oven for all of your cooking needs.  These are both found in a slide out along the curb side.  A center island features a double sink, plus added countertop prep space.
Opposite along the road side another slide with a free standing dinette and theater seating for two.  You can opt. for a super sofa instead.  An entertainment center with an LED TV and fireplace below are along the angled outer bathroom wall and easily viewable from the seating in the room.

Head up the steps to a front master bedroom and complete bath. The bath is found on your right at the top of the steps up and includes a large shower with skylight and seat, linen cabinet, toilet, and vanity with vessel bowl sink. A second bath entry door slides to allow easy access right into the front master.

In the bedroom you can easily rest and enjoy a little down time. There is a comfortable queen or optional king size bed, dual nightstands, overhead cabinets, and a slide out closet with drawers for all of your clothing storage.

You will appreciate the convenience of the unobstructed pass-through storage compartment when loading and unloading your outdoor gear, plus the universal docking station, and much more inside and out!

Blue Fox Rv 

390 W 2500 N North Logan Utah

435-890-4602

435-317-3625

STOCK #206357 VIN 573FM453XJ1206357 LOT North Logan, UT, 84341

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Towing & Dimensions 5

GVWR 20000
Dry Weight 15900
Hitch Weight 3400
Length 520
Exterior Height 161

Tires & Wheels 9

Rear Tire Westlake® G-Rated Tires
Rear Tire Width 235
Rear Brake Type Electric Drum
Rear Tire Aspect Ratio 80
Front Brake Type Not Applicable
Wheels Composition Aluminum
Tire Brand Westlake®
Spare Tire Location Exterior Mounted
Rear Wheel Diameter 16

Cargo 4

Cargo Area Flooring Type Vinyl / Carpet
Cargo Area Width 96 / 2438.4
Cargo Area Rear Door Style Ramp Door
Cargo Area Length 156 / 3962.4

Quick Overview 8

Parent Company Winnebago Industries
Year 2018
Make Grand Design
Display Name Momentum 399TH
Class Toy Hauler
Max Sleeping Count 9
Number of Slideouts 3
Introduction Year 2016

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You're inquiring about
2018 Grand Design RV Momentum 399th
$64,995

Local. Honest. Built to last.

Most of our buyers come from referrals because we sweat the small stuff after the sale.

Family-owned
Local to N. Logan
Not corporate
4.8 ★
247 reviews
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Inspection
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Pricing
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On-site
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Quick answers, no sales pitch.

What towing capacity do I need for a RV?

Most RVs require a vehicle rated for at least the unit's GVWR plus 1,000 lbs of margin. We'll match you with units your tow vehicle can handle.

Is the 2018 Grand Design RV Momentum 399th still available?

Yes — as of June 24, 2026, this unit is on our lot in North Logan, UT. Last updated June 23, 2026.

How much is the 2018 Grand Design RV Momentum 399th?

$64,995. With $12,999 down at 6.99% APR over 180 months, that's about $467/mo. We accept trades — talk to us about your current unit when you visit.

What can tow this Grand Design RV Momentum?

1-ton truck with a proper heavy-duty towing package required — F-350+, Silverado 3500+, Ram 3500+. Dry weight is 15,900 lbs. Hitch/tongue weight is 3,400 lbs.

How many people can sleep in the Momentum?

9 people comfortably. Bed configuration: 1 queen, 1 bunk, 1 sofa-bed.

What's the warranty?

Basic warranty: 12. We'll go over all coverage details at the walkthrough before delivery.

Can I trade in my current RV?

Yes — we take trades every week, even if you don't buy from us. We'll give you a real offer once we see the RV. Call (435) 317-3625 or fill out the inquiry form below to get started.

How do I schedule a walkthrough?

Call (435) 317-3625, or fill out the inquiry form below. Same-day response during business hours.

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