On my 65 I plan to add a fuel cell between the rear frame rails where the spare would go. I have seen guys put Blazer/ Suburban tanks back there. I had a 66 C20 that had dual saddle tanks mounted. It was a very clean mounting job. The tanks were installed on the truck back in the late 60's and were made of heavy gage steel. They had locking fuel doors cut into the bed. It had a switch on the drivers side floor to switch the tanks. I saw a lot of pre '72 trucks out in the western states with that added to them.
