Well, i know it is always made overkill. However. My 180 sits on 3/4" ply, 1x1 triangle braces in the corner. top, bottom and sides are plywood, no additional bracing between doors. it is pretty much sitting on plywood edges.
the tank load is static, meaning not in motion. plywood is very strong used this way. key is to seal it so it case of major leak, it wont seperate. with the stand being pretty much boxed in, it holds itself together.