Thanks! Since I made the original, I’ve made one important improvement to the case design: I’ve used a deep engrave to remove about half a thickness of the puzzle frame and case back along the edges where the case cover snaps on. This lets the case cover snap closed as on the original design and also lets it snap neatly onto the case’s back when the puzzle is in use. Here’s a picture:
The upper drawing, shows a cross-section of the edge of the case with the case cover in place. The lower drawing shows the case cover snapped to the case back. The places where the case cover grips onto the case back (in the upper drawing) or the puzzle frame (in the lower drawing) are made using a deep engrave.