As far as strength of the stand, most of the weight of the tank is supported in the corners. My 55 gallon stand has no back in it, and things are fine. There is a brace in each corner on the back side and that's all the support the is given on the back. I also agree with everyone else, that evaporation is a good thing. Plus the open air allows the water to oxygenate better. Isn't that why people use things like eggcrate instead of glass covers?