The generally held wisdom is that a rimless tank should have a layer of foam underneath it because the full bottom panel sits flat on the stand; whereas a rimmed tank should not because it just rests on the external rim. While many manufacturers of rimmed tanks do not recommend foam, a few custom houses do (Glasscages and apparently Leemar). Assuming one selects the foam sensibly, I have frankly not found arguments against putting foam under a rimmed tank compelling, so I do it. Don't think I've run any of my tanks since about 1990 without foam.
But, I would hate to recommend that someone put foam under a rimmed tank, have it break, and then have no warranty recourse - so rather than listen to opinions here on RC, seems to me the best approach is to follow the recommendations of the tank maker (even if knuckle heads like me choose not to).
Spoke to marineland, they say no foam, cause the sides can "sink in" and the foam would then put the pressure on the centre beam at the bottom, which is not supposed to have any weight on it ... saying this can crack the bottom ...
but yea ... just what they are sayingfor what ever that is worth.