Don't sand free hand. Draw guide lines top/bottom/front edge and use a long block to even the bevel after planing. My favorite block is a piece of 2x4 cut to fit a half sheet of sandpaper with one side planed/belt sanded flat. The half sheet is pulled up the sides and thumb tacked to the block making a very controlable/versatile 9"x 3.375" sanding tool. Just tear the sandpaper using a straight edge on the back side.

Terry in LP