Floorboard repair
As a long time caroholic who's also in the "business" let me give you my honest advise, although it may not what you want to hear.
Living in California, I'm spoiled with a mild climate and 300 days of sunshine a year, but not long ago a bought a 1971 Dodge D200 pickup with super low miles coming from Oregon. Usually I don't buy non-California vehicles, for obvious reasons, but on this one-owner truck, with original paint, I couldn't resist.
Body was rust free except for one hole on the floorboard, pretty much where the cab bolts to the frame. I contacted an expert welder who usually only restores old Porsche 356s, and asked him to help me out. We removed the bolt, supported the cab, cut out the rusted metal, and he replaced it with a new one that he hand-formed, then butt-welded. If you don't know, you'd never know, except that we had to paint over the new area to prevent it from rusting again.
Point to be made: spend 2 hours worth of expert labor, money well spent, and assist the pro by helping and observing. Beats a crappy patch any day.
Good luck!