Super55 you guessed right. I lined it with a flexible PVC roofing product that I had scraps of laying around. I glued the sheets and walls and rolled them into place. Then all the seams are heat welded with a hot air gun and a rubber roller to press the two together. Ive seen it lately being used for shower pan liners, although Im not sure if that type can be heat welded. You could also use EPDM, which is typically used for pond liners and tube tires, etc.

It works like a charm. I use old seat frames for the positive end since they have a lot of surface area available and can easily be tossed on the ground to knock all the rusty gunk off. They last a fairly long time. One other thing, I used scraps of old carpet to line the bottom so that I had no chance at poking holes in the PVC.

Jeff

My 1953 Chevrolet
1947.1 Gallery
1972 C-10 1/2 Ton & 1972 C-30 1 Ton