That totally sounds like the answer. Having more water in the bottoms of them will probably make them less likely to lose their air if (when) someone runs one over and traps it under a tramp.

It would be nice if you could get ahold of one to test out before you have to commit serious currency. Tie some flotation to it and try all the worst-case things you can think of (short of cutting it, of course) and see what happens. It would be even better for the company to do that themselves and add it to their promo videos.

Mike