I agree with Uncle Bob. My first thought when you mentioned tarping was condensation being trapped and collecting on the underside of the tarp. My barn floor will sometimes sweat, like with weather changes. Tenting would eliminate that problem.

I'd heard before that primer can absorb moisture, and have seen primed steel bodies surface rusting when a guy would prime and drive (especially the old light gray stuff) but I'd never heard before that the primer that gets wet needs to come off and be reapplied before painting. I don't doubt it at all, but that's harsh!

I wish I'd read all of this stuff before doing any work on my cars! I'm about ready to grab the belt sander....