2025 Grand Design Solitude 345GK vs 2024 Grand Design Momentum 399TH

Detailed Comparison

Comparing the 2025 Grand Design Solitude 345GK to the 2024 Grand Design Momentum 399TH reveals some interesting trade-offs that could influence your buying decision.

The Grand Design Solitude 345GK measures 37.0 ft in length at 10,000 lbs, compared to the Grand Design Momentum 399TH's 28.0 ft and 8,300 lbs. GVWR ratings sit at 13,900 lbs and 11,900 lbs respectively.

Capacity-wise, expect to sleep 4 in the Grand Design Solitude 345GK versus 9 in the Grand Design Momentum 399TH. With 1 and 0 slide-outs respectively, the parked floor plans differ significantly.

Tank capacities are a key off-grid consideration. The Grand Design Solitude 345GK carries 56 gal of fresh water, 61 gal gray, and 40 gal black. The Grand Design Momentum 399TH offers 68 gal fresh, 70 gal gray, and 50 gal black. The Grand Design Momentum 399TH has the edge for extended dry camping.

Budget-wise, the Grand Design Momentum 399TH is listed at $61,000 compared to $162,000 for the Grand Design Solitude 345GK. The $101,000 difference could cover upgrades, accessories, or several seasons of camping.

For family camping trips, the larger floor plan and additional berths make a real difference. For boondocking, the model with superior solar and battery setup will keep you comfortable off the grid longer. If you're going full-time, the larger tanks and more robust build quality matter enormously.

No comparison can replace walking through each unit yourself. Visit a dealer and experience the layouts firsthand.