On this occasion I repaired the driver's side floorboard of my pickup using only scrap metal taken from a leaky fuel tank I happened to have lying around. But first a little background on this truck. My Dad bought this thing for $600 in 2003. This was before I got involved with auto repair, and consequently, he did not consult me on it's mechanical soundness before purchasing. It had a blown head gasket and cracked head. I put an engine in this thing some time in 2004 and returned it to him. It was a second vehicle for many years until I asked to borrowed it in 2013 and he simply gave it to me. This is what the floorboard looked like underneath the carpet.
Several years prior, I'd replaced the fuel tank in my B-body dodge van, and still had the leaky tank hanging around. I decided, since it's a fairly rust-resistant alloy, to use it as the patch material. After a couple of hours of measuring, cutting, stretching, shrinking, and welding; the floor is whole again. Only this time it has some amount of corrugation.
The weld quality is poor, partly due to the degraded quality of both the base metal (I hadn't removed all the corroded material, just the parts that were very flimsy) and the patch material; but mostly it's due to the 110v flux core (no gas) mig power source I was using. It cost less than $200 new. One does get what one pays for, and this case is no exception.
Here is the repair again in 2017. The brown is Rustoleum "rusty metal" primer.
This repair was very inexpensive. A few ounces of flux core wire, some time, and a piece of scrap metal. There is something very satisfying about achieving results with no material investment. The primer I applied when I did the whole truck exterior in it.
More images in the gallery.