1965 barracuda spare tire cover question

Hey wondered if anyone could give me insight on the panel that is carpeted over the spare tire. Mine did not have one. I’ve seen in other posted it’s carpeted but what is the size and shape and material that the carpet sits on? 1/4 plywood or card boardish material? My trunk area was a mess but because of the factory seam sealer it wasn’t all that “holy”. Thanks everyone. Appreciate all the questions answered.