I went to Home Depot and bought insulation board. It is foam board used in walls. It was a tad too tall, so I asked the clerk to cut it down for me. I did enjoy the look I received from the clerk when I explained what I was going to do. Once he got over his desire to giggle (or roll his eyes), he suggested a damaged piece of insulation board. It wasn't going to sell and the damaged part was removed when he cut it down for me. I got what I wanted cheaper and he got rid of damaged merchandise. Win-win.

I covered it with felt by pushing pins in the outside edges and taping the fabric to the back. If I had to do it over, I would probably use flannel. But, hey, the GREEN felt (with little flecks of gold) was on sale and we all know how we get when fabric is on sale.