[davocean]

While the tank itself does not need bottom support like a rimless or non trimmed tank, that does not mean a ply top will harm it, and in adding a ply top it usually makes the stand itself stronger.

Years ago we saw debates over the foam padding(still a little today but more so back when)
I guess there were cases of people using foam padding thicker than the air gap space that will be under your tank bottom.
Thicker padding than that space can cause reverse pressure which conflicts w/ the design.
So this rep may not have understood or answered your question properly.
If you add a ply top and it covers the entire perimeter, so trim sits on top of that, your bottom panel will still remain suspended, it's like a 1/2" space or so, if that bottom panel flexed more than 1/8" or even a 1/16" I'd be surprised, so in other words far from touching or being an issue.