[RVANANO]

I think I may have figured out the problem. When I try and lay a level across the width of the 3" steel tubing, I can rock it. So the outside of the steel isn't perfectly flat. It seems since the steel frame is just a hair smaller than the tank frame, the tank is only touching various high points of the frame but is still level. I am thinking in that case, the plywood or even a solid wood frame to go on top would be the ideal solution to create a level surface for the tank to sit on. If ply, I would choose the really good stuff made of more layers.