Hey. I grew up on a sod farm and LOVED to replace the carpet with the thick 'construction' mat.
JC Whitney used to sell long ago but I think that ACC (auto custom carpets) still sells a heavy duty rubber matting to cover the whole floor. Even under the seats!
You might even see their stuff on Ebay with others that might get you what you need.
(I'm going the same route with my '64 2-ton)
It's just breathing that rubber smell for months during the HOT Memphis temps.
IT GETS EVERYWHERE.. YOUR PILLOW WILL START TO SMELL LIKE RUBBER.

Errol