It is not the easiest or the fastest solution, but on my last truck I used rubber matting for horse stalls. The stuff is bullet proof and relatively inexpensive. Rural King sells it on 6' wide rolls. You can buy it from 1/4" up to 3/4" thick and purchase by the foot.
It is definitely not the easiest stuff to work with if you are trying to mold it to curved floors, but is awesome on a flat floor. On the curves its sheer weight makes it pull down and mold well given time, but it is a wrestling match at first.
