[karimwassef]

I'll take some pictures with dimensions to help.

The plywood isn't cheap, but with a 12'x8' tank, I can get a single sheet to cover the span.

So I use 3 full sheets and overlay glue to create a solid sheet. I had a thought to pre-stress the sheets by slightly bowing them upwards as I glue them but I decided to avoid that complexity and risk.

So 3 sheets then an overlapping 3 sheets cut to cover the seams, then 3 sheets over that covering those seams, then 3 sheets over those cover those seams. So 12 sheets in total at 3" thick with all seams double covered. That's $480 in plywood for the base!

Not cheap, but I think it should hold a lot of weight, especially with 2x4s under it again.