I wouldnt worry. the manufacturers tell us that glass tanks technically only need support on the corners. as long as the tank is level and flat, you should be fine. its likely not the tank that is the problem, rather the wood warping. I have had tanks set up for years and years, with the same type of small gap. as long as the tank is level and flat, you shouldn't have a problem.
also, if your tank has a 'floating bottom' - ie a plastic center brace on the bottom of the tank as the top does, stryofoam is not recommended (so say the manufacturers). I don't use styo either. I have had tanks for 20 years now. but they are alway level and flat.
even if your tank is like this, you might be okay