That is dependent on how you treat the bare metal, here you can have steel zinc blasted, so a coating of zinc is blasted onto the bare steel and won't come off . My Z suspension springs are bare (no paint/powder coat), and after 12 years still no rust. Not saying "its the way to do it" but there other ways to do things.
Nice work by the way ND240Z, makes me feel like the body of the csp I am restoring isn't that bad (but it is).