epoxy paint ?'s

Lots of times a "restoration" job takes time... hence a panel sitting in bare metal for a few days minimum... your moisture,oil, contaminants, don't need to penetrate from the top down. A panel will actually start corrosion in a very short amount of time. The rusting issue will come from beneath not from the top. A good body man can do filler work on top of bare steel with no corrosion issues. I have done it for 15 years with no rust issues ever. As long as the panel is coated quickly without sitting for very long it will be just fine.