I would apply epoxy primer to the bare metal. It has the best corrosion resistance and does not need to be removed for your finish coat. When you are ready to do your body work or finish you will need to sand the epoxy then apply another coat of epoxy before going to your finish work. I assume the body will be out of the elements in a garage? No primer holds up to sunlight very well since it is not a finish coat.
I hope this is helpful.
Regards,
Steve
New Orleans
