I have run out of bottom boards, so I thought I would try building some. I don't have a router to cut out the inset in the side and back rails, so couldn't I just use 3/4" exterior plywood for the bottom and cut side and back rails that give me a 3/4" opening that I can leave open or put a reducer in? I have never flipped my purchased bottom boards to use the smaller opening, so why have it?