Given the fact that only the plastic rim or frame touches whatever the tank rests on, foam really isn’t necessary provided the surface is smooth & level.
All the tank weight rests on the frame, which in turns needs only a flat, smooth, level surface to stand on.
So I have never used anything under framed tanks except for a cut to size piece of plywood, which helps protect the surface & does a decent job of soaking up drips without deteriorating like particle board or MDF etc, if it has to.
Though I generally cover the plywood with clear heavy vinyl sheet so it won’t get wet either.