Foam under tank

[streetrodder007]

I personally don't think your glass should bow or move that much, the benefit of foam is that it is a pliable and a slightly flexible support if you should need it, or too make up any difference in imperfections when the tank is manufactured. Foam is good cheap insurance.
I can see this moving glass issue being one of those topics everyone would argue about in different ways. Just like I don't use a skimmer- and some people look at that like I'm crazy.