Why it's worth it
The FIVKLEMNZ holds a week of luggage for a family of four and mounts on a car with no roof rack at all. Welded seams, ten straps, six door hooks and an anti-slip mat come in the box, so there's nothing extra to buy.
This is the bag that fits the most cars and the most stuff. At 52 by 40 by 18 inches, it's rated for four to six suitcases, which in practice means a family of four can pack for a week and still see out the back window. The ten reinforced straps and six door hooks mean you don't need a rack, crossbars or side rails. If your car has doors, you can mount it.
The waterproofing is layered rather than clever. FIVKLEMNZ uses 840D PVC with high-frequency welded seams, so there are no needle holes in the shell for water to find, and then adds a second waterproof cover on top of that. Owners who've driven through desert heat and multi-hour downpours consistently report dry luggage. That's the pattern that matters more than any single claim on the box.
From our review of 6 waterproof roof cargo bags, by Ben Carter, Tech Editor