For my CJ, I bought some pre shaped ones from JC Whitney. They are hevier guage than stock, so I am happy with that, but I was dissapointed with the way they fit in. I was expecting a more or less "lay in", and they were not that. What I ended up doing was this:
Step one: Cut out old rust spots, leaving what was left in more or less straight lines, so that when I was done I could seal up straight areas and not all kinds of shapes
Step two: Lay in the floor pan, then start beating on it with a BFH. I fould that if I could put the pan in more or less the right spot, then bend one corner to lay down were it belonged I could then weld that corner in place. I would then use the hammer (a ball pein hammer worked great at bending the sheets into place). I would shape / weld / shape / weld as I went along.
Step three: I used a 2x4 and a floor jack to then jack my old floor up against my new floor and I was then able to weld across those straight lines (See step one) and completely seal off the bottom of the floor as well.
Step four: From an auto body supply shop I picked up a tube of seam sealer, it comes in a caulking gun and was about $10 per tube. It is the stuff they use to seal the corners of pick up beds that holds up for years, and stays a little soft. I used that to plug up any areas that I could not weld shut or were difficult to weld
All in all I am very happy with the final project. It took much longer than I expected and there was lots more cutting / hammering that I expected. My first pan took an evening to get in place, and the second was a little quicker.
