The side of the sander that is facing down, is purt near flat. It has a triangle shaped cover for the belt that makes an approx. 5" per side triangle. It is held on with three screws with threads similar to a wood screw that are about 1/2" long. I just drilled matching holes in the 3/4" plywood, and run 3 wood screws 1-1/4" long and the same diameter, right through the holes of the plywood, and through the cover, and tightened them up.I had to shim the one hole to make it square with the little table I made for it, with a simple flat washer. Also, the cover was vented, so i drilled a couple 1-1/4" holes in the plywood base to help it get some air.
My only complaint, is my vacuum don't pick up like it should. I'm gonna have to cipher a remedy for that. Maybe I'll find some use for duct tape!