I just finished replacing the disintegrating balsa wood piece under my cargo area carpet with black ABS.
I have not seen a thread on this so hopefully this can help someone. I started with a piece of ABS 48"x96"x3/16".
The bottom near the tailgate is 48" wide I had to add 2 pieces on on each side, those pieces are approximately 5 1/2"x 20". The measurement at wheel well to W.W. is 43" wide.There are 2(ea) 5/8' holes at the top where the seat belts bolt in, they are 16" from center of hole to W.W.(Right & Left). U shape cutout for the rear seat post at the top are 2"x2"
I used a razor blade to etch out the cuts and then broke off the pieces.
and then used a dremel to finish off the edges. If I have forgotten something or you have questions P.M. me.