I like powdercoat, but this is probably not the best item to use it on....once you damage powdercoat, moisture can wick in under the coating....depends a lot on how well they're coated.
Personally, I'd VHT them.....some light etch prime, then hit them with VHT spray cans....the GM Satin Black engine enamel is awesome...it covers great, its reasonably tough and its an easy touch up. VHT also do a "Small Engine Case" flat black, which is for painting motorcycle engine cases etc...pretty tough stuff. If you like the wrinkle finish style, use VHT wrinkle black....but apply to a warm item, and use a heat gun on low to bring out the wrinkle finish in a consistent manner.....without the heat gun, I've found the wrinkle paint to be very patchy in how it turns out.