Thanks for the response everyone! I can tell I'm going to love this site. The West System guys wrote me back and suggested attacking it with the sandpaper once again but using a jointed board to help get the flatness I'm after. I'm going to get things as close as I can once again with a laser (by hand) and then run the length of it with a jointed board for awhile and see how that turns out. I'm hoping with consistent pressure it'll take care of high spots.