The last I was involved with Class A finish coatings, the following treatments and layers were involved for sheet panels:

- zinc, or zinc-rich coatings (either galvanized or galvannealed)
- phosphate
- E-coat primer
- color coat
- clear coat

When a panel is repaired, you lose the first two coatings, plus the efficacy of E-coating. I've seen and used phosphate solutions for bodywork, but I can't imagine that they are just as good.

If you do repair the panels, the corrosion resistance will be no better than with cars from the 50s and 60s. And we know how quickly those cars rusted. My dad told me stories of how wastage was so great that he had to have new rocker panels welded onto his 55 Ford every 18 months.