my polished SX has lasted 3 months of welsh wetness. with zero protection washed with a hose pipe also the frame was highly polished with a polishing mop. on a grindstone wheel,
still just as shiney as the day i polished it.
the more polished the frame is the longer it takes to corrode.
Just a thought, but could you not just laquer the frame then wrap it in that heli tape stuff that you can get ? That will stop it from peeling and will protect it no ?