Strange world you're from, where only solid lumber warps (commonly used to construct things like floors and other weight bearing elements of structures) and plywood doesn't.
Whatever its made of, the top will have to be properly supported by the blocks underneath.
I think some more pictures would help to illustrate what I'm saying.
View attachment 1443557
View attachment 1443558
View attachment 1443559
View attachment 1443561
I consider the cinder block stands above, some with ply some with lumber, to be well built, while the one below, with only 2 pillars and the double layer plywood, I would consider unstable, prone to failure:
View attachment 1443560
Such a skimpy design would only be adequate for tanks 10-40 gallons imo. With the 72 gallon you're gonna want a very stable platform.
2x10s with cinder blocks on both ends and the middle with almost 1000 lbs of weight on them will not warp, even if they're still wet when you first set it up. I can guarantee this.
A foam layer will not be necessary with a tank of this type. The tank is fully encased in the plastic trim and can rest right on the wood.
Backfromthedead
we have all made trips to the lumber section and sighted down a dimensional piece of lumber to ensure straight, not cupped or bowed. Unfortunately, dimensional lumber is less dimensionally stable than plywood over the long term. Use of dimensional lumber set on edge is different than laid flat. Will each of us have the same experiences with a supporting piece of wood failing or causing a tank to fail?
