I may have found a solution, I installed the flexwatt like normal, but I'm thinking of putting down 2 3" sections of eggcrate on top of the flexwatt and on the other side. This would save wear on the flexwatt and raise the tub. The eggcrate is 1/4" thick. For those of you who don't know what it is, heres a pic. I'm worried though that I won't a warm enough hot spot. I'm using 11" flexwatt.