This thread definitely has peaked my interest. I usually put about 1/3 tank of fresh water when traveling for the pit stops. And I've definitely towed with black and grey tanks pretty close to being filled, due to not having anywhere to dump. I always worried more about the extra weight being towed, never crossed my mind that the manufacturer of this expensive trailer wouldn't put good enough supports for it... I guess I should go ahead and pull the coroplast to check them out, I do need to find and check my rear auto level sensor anyway, just didn't want to have to remove the plastic under there yet!
On a side note, I do know that the generator and fueling station fuel tanks appear to be secured to the frame very well, and the tanks themselves are metal.