Both the inner and outer metal of the fender lip was pretty rotten so had to be replaced
Pretty happy how it turned out. You wouldn't think it (I know I wouldn't have) but just this one patch took me a couple hours. There's a mild "s" curve to the backing piece and the upper piece had to be arced just right to keep a consistent gap along the skirt, then welded together, ground, slot cut for skirt pin, and welded in place. If I was a pro it'd probably go a lot quicker but still, I've definitely gained an appreciation for why proper rust repair is so costly.
Substantially more difficult was creating the piece to repair the inner fender. I will make it out of 5 pieces of metal because of how crazy and complicated it is. This is actually my 3rd attempt which is finally working out. The problem with the first two attempts is that the fender lip would flex a bit as I tested fitted so I could never get it to fit properly. Eventually, I had the revelation to weld a little strip metal onto the lip to keep it in place and that made all the difference. Including the time wasted on the failed attempts, I've probably spent 6 hours on this piece so far and it will take a couple more to finish it off and plug weld it into place.