2025 Grand Design Solitude 390RK vs 2024 Grand Design Momentum 399TH

Detailed Comparison

The 2025 Grand Design Solitude 390RK goes up against the 2024 Grand Design Momentum 399TH in this detailed comparison. Each has distinct advantages worth considering.

Starting with size, the Grand Design Solitude 390RK measures 30.5 ft long and tips the scales at 15,400 lbs dry weight. The Grand Design Momentum 399TH comes in at 28.0 ft with a dry weight of 8,300 lbs. That gives the Grand Design Solitude 390RK roughly 2.5 extra feet of length.

The Grand Design Solitude 390RK sleeps 10 while the Grand Design Momentum 399TH accommodates 9. Slide-outs play a role in livability: the Grand Design Solitude 390RK has 4 and the Grand Design Momentum 399TH has 0.

For boondocking enthusiasts, tank sizes matter. Fresh water capacity goes to the Grand Design Solitude 390RK at 70 gallons versus 68 gallons. Solar-wise, you get 400W on the Grand Design Solitude 390RK and 200W on the Grand Design Momentum 399TH. Battery banks are 300 Ah and 150 Ah.

At $62,000 MSRP for the Grand Design Solitude 390RK and $61,000 for the Grand Design Momentum 399TH, the Grand Design Momentum 399TH saves you $1,000. With only a 2% price difference, the choice comes down to features rather than cost.

If you're traveling with a family, look for the model with more sleeping positions and better storage. Boondockers: look at the fresh water capacity and solar/battery systems — they determine how long you can stay out. For the full-time RV lifestyle, every gallon of tank capacity and every inch of counter space counts.

The numbers tell one story, but the feel of a floor plan is personal. Schedule a walkthrough before you decide.