Like just mentioned, old school is filler over CLEAN bare metal. He said he had seen it be good after 20 yrs. I bet the key there is CLEAN metal, New way of epoxy primer over cleaned metal, then filler The epoxy seals the bare metal, and sticks well. The filler needs some time to shrink. The better the filler the less shrink? Then high fill primer, seal with reduced epoxy, topcoat. That is many people's method.
