The next part was simple... the edge of the case is aluminum and has a little radius in each corner. I measured the case and ordered the piece of plastic. I wanted something thicker so the kids wouldn't cut through it of break it easily by pushing; so I used 1/4" thick Acrylite (lets light through). This piece was almost $20. I tried to talk them down, we brainstormed ideas, I negotiated... nothing. I had to spend the $20.
Used a jig saw to cut the radius's for the corners and the notch for the lid support.
Note: make sure you keep the protective covering on. Ask me how I know this.