No, you do not need bottom trim. I would build a sturdy stand with 3/4" plywood across the top (where the tank will sit), then put a piece of styrofoam insulation on top of the plywood to even out any irregularities.. so it will look like:
Tank->Styro sheet->plywood-> stand base. Obviously, the stand base would need to support all edges, I would probably add middle support too in the base.
Do you mean a stand edges would give support like the trim normally would? In which case i agree. I know people have had good luck with no support top OR bottom w/just silicone, but you dont have the same level of safety.
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