[azmike]

You all may know and use some fashion of this--but if not, its just a tip from a newbie that it works for. I don't have a belt sander and found this is one way to work on the finish.
I have a block of the dense, black, closed cell foam insulation (armaflex), about 2" wide x3" high x 4" long-cut it dead center on the 2" about half way thru and full length. just take your sand cloth/paper (sized to fit the full length/depth of your cut-when folded in half) slip it in with the abrasive sides facing and slide in the blade. hold the block and slide the blade / hold the blade and slide the block - edge up or down, changing grits as you go --- just like your using a saw.
give it a try--azmike