just paint them, the powder coating will wear off in the same places that the paint will so dont waste your money on the PC job. just clean them really good with some soap and water, sand and scuff any bare areas or areas with chips or nicks ect, then use a good self etching primer and give it a few light coats (as instructed on the can) to give good full coverage then let that set up, lightly scuff that and spray with desired color epoxy paint, that will be your best bet against road spray and debris.
-i use epoxy paint on all my frames and metal under the truck, like axles ect. typically i get under my truck once a year in the late summer and spray all exposed metal that has been scrapped or bashed on rocks, giving it a good seal for winter, that way i keep any major rust issues from ever happening. i have never had a vehicle that has rusted out on me, and i lived on the coast for a few years and was driving my old 85 truck back then. its frame and everything under the truck looked better than the rest of the truck, and is even in better condition than the 85 truck i have now that has been in eastern oregon(high desert) 90% of its life. epoxy paint is tough as far as rattle can paint goes and its dirt cheap compared to PCing