I have not read of any needs regarding the actual size of your tank when having sponges. High water flow, high light (as many are photosynthetic) and feeding frequently (phytoplankton, oyster eggs, rotifers and other filter feeder food).
The only problem I would see is keeping your parameters in check with such a small tank.
Any sponge pros out there want to chime in? Interested myself.
I was just curious because most of the sites you can buy them from say minim size of 60gal but I don't see why it would make a difference. They are stationary, I would think it would only be an issue if they moved and came in contact with say an anemone or something like that.