The tank rests in two cradles that allow for some rocking movement from front to back. It's just held in place with two flat spring steel straps that are cinched down tight. Loosen those up and orient your tank to the proper straight up and down position and then cinch them up tight.
The tank sits on pads made of roofing felt or some such. If it's disintegrated, the tank may have loosened up and moved.
I used peel and stick flat roofing material in place of the felt when I put in the new tank.
