Step 4: Build a mounting panel
Next I made a wooden panel to fill the opening of the cut suitcase. This panel has two purposes: (1) it reinforces the opening (keeps it from sagging); and (2) it provides a means of mounting the suitcase on the wall.
I made the panel from some scrap plywood I had left over from a previous project, and outlined it with 1x2 pine (to provide a place to screw the suitcase onto). I could have used thicker plywood and omitted the 1x2 strips, but I decided to use what I had, which was a bit thin to attach the screws to.
I pre-drilled all the holes, but didn't attach screws into the lid of the suitcase until after it was mounted (you need to get inside the suitcase to screw it to the wall).