The pylwood being larger than the tank footprint is not the issue. The possible flex or delection of the plywood without a support under its edges is highly significant. DIY is great if you have the engineering know-how and references to back it up. My tank room is more than half DIY stands, but I had the engineering back-up to be secure with the structure. An unsecured unupported piece of 1" ply is not suited to a cantilevered stand IMHO.