I went ahead and filled the tank with water to check how it sets down on the frame and ran into a concern. Before filling with water, all four corners had a slight gap from the corner to about 6-8" inward towards the center. I could fit a .035 shim all the way to 8" in from the outside edge of each 6 foot side basically. The builder said he designed the frame to have slight positive camber so it would deflect and be level when filled. That gap is almost completely gone on all corners but the end that drops off (not the end that overhangs for plumbing etc), I can still barely get a .020 shim to slide in from the corner to about 2-3" inward. The opposite corner has a slight gap as well but much smaller. If I get down to where the tank frame meets the metal stand frame, I can see a gap the entire 3 foot length just a little bit inward from the edge. What are the thoughts on this? If I shim the bottom of the stand up, I don't think it will address the issue b/c it's steel. I was told not to lay plywood down under the rimmed tank b/c it could possibly start to crush the edge of the ply and cause uneven pressure. The tank is perfectly level in both directions.
