I put rear mounted fuel tank in my 37 pu years ago.I bought a universal tank from "Tanks". The job was easy since the bed was off the truck at that time. I liked the smooth look of the 16 guage welded steel tank.Phat's point about the gas spillage should not be taken lightly.In a low speed roll over ,which is a common accident in a truck, the filler neck breaks or the cap flies off spilling fuel on YOU.So there you are,safely hanging from your seat belt ,soaked in unleaded. Panic time?In the late 60's ,a series of drivers burning to death after surviving the initial accident,pushed truck makers to relocate the gas tanks out of the cab.But, our other 3 Stovebolts, still have cab mounted tanks, Oh well.