That's a pretty common complaint around here. The tank is manufactured flat on all sides, but it's pretty thin and therefore bows under the weight of the water. Since it's only supported on the sides the bottom bows pretty significantly. Supporting it better won't hurt anything and may save it from falling out, which is another complaint.
Salem 29RKSS Pushing a 2500 Mega-Cab CTD!
Gotta go campin!