FYI, I've read numerous stories of mouse pads leaking chemicals into a tank (glue between the neoprene and the surface material). No big deal under the sump, but I wouldn't put one in the sump. If you really want to get a neoprene pad try to find a used wet suit or pure neoprene material instead of a mousepad. Or you could just use some thick silicone feet on the pump.