So SNKEBIT, are you using those spot weld drill bits to get rid of the old welds? I went through a bunch of them when I did the Charger and hated them. I tried a couple of different brands. Sometimes they'd snap off on me on the first weld. I always hoped there was a better solution.
So much of my flooring was rusted away that I skimmed some panels off with a torch instead. - But in the areas that had solid sheet metal the surfaces were so far from flat that the bits would want to wander or they would catch unevenly and break a few teeth off.