It's nice to see my husband was so happy with my desk purchase!
I think the back panel lining turned out great. I used foam core covered in fabric. (I bought a piece of foam core that was 4 feet by 6 feet. You should have seen me carry that around the store and load in my van without bumping or dinging it on anything.) I cut it to fit, then hot glued the fabric around on the back of the board. It was a little work to keep the pattern straight. I had to pull it along. Then I just pushed the piece back in and it stayed in place all by itself. I used 2 layers of foam core on the bottom so that I can use push pins in it. I think that cute wrapping paper or wall paper would work too.