caprice wagon cargo mat

I just got a beautiful caprice wagon and I'm looking for a cargo mat that would cover the rear with all the seats down. I bought this car to haul a trailer and other junk, but the more I drive it the nicer it seems to get!
If I could get a roll of some kind heavy duty rubber or plastic I could custom cut one. Any ideas? Thanks
Jerry

I used a carpet remnant. I also tried a vinyl floor runner. I liked the carpet better and it kept things nice.