What should I put here now?
 

I have had the rear seat out of the Mustang for about 6 months now. I am trying to find out what everybody has put back there in place of it. Did you use sheet metal, thin plywood......? I am open to any suggestions. I would like to keep is as inexspensive as possible, and fairly light. I am tired of looking at the spare tire hole and the half carpet half metal floor. I will carpet whatever I install though. Thanks for any suggestions!

Chris