Installing new carpets

I used this behind my rear seat on my 68 Hardtop Dart. Not cardboard. Check your measurements. This is 2'x4'. Not sure if you need bigger. You could always spray it flat black.
Handprint 1/8 in. x 2 ft. x 4 ft. Tempered Hardboard (Actual: 0.115 in. x 23.75 in. x 47.75 in.) 109112 - The Home Depot
Thanks, I actually purchased this material to make new kick panels for the front. I think it's a little too thick for the back of the seat which folds down to extend the deck area. The piece that was in there measures .05" thick but it pretty much desintegrated when I pulled it out. The same material was used for the deck area and it was pretty much dust when I removed it. I can see that it would be ideal for the back of the seat between the cab and the trunk on your car.