I used a 5/8ths MDF board I think the size was, that I got from Lowes. It was like $25 or something like that for a 7' sheet. I made it in one piece. I took the side pieces out the trunk and the back piece. I then took some bold measurements to get it to fit in there and just started trimming where needed. The edges didn't have to be perfect since the side pieces and the back piece were going to cover the edges. I used "The Great Stuff" to seal it to the floor and trimmed the excess off where necessary. Then I bought some carpet from Wal Mart and laid down some glue to the board for the carpet to stick nice and tight. Then install the pieces that I took out. I had to trim the bottom of the back piece to get it to fit properly.
Brenton
Brenton