Why paint at all? unless you want to disguise the fact it will be on a galvanised chassis
All sorts of galvanised things get like trailers get left unpainted, is there any evidence to support the fact that painted galv lasts significantly longer than unpainted?
Because re-galvanising things is a lot of work and it does eventually fail without protection. I've got some rotten galv gates and my galv trailer is now rusty especially where it's been blasted by stuff off the back wheels of the car.
Paint or any other protective coating will 1. provide increased abrasion resistance thus stopping the zinc getting literally blasted off (zinc is quite soft) and 2. Will act as an isolator to stop the zinc reacting/ weathering. Once the coating is chipped, the zinc will begin doing it's job until it either runs out and allows rust to start or until you top up the coating. I know I'd much rather top up the coating than wait for the often large scale job of getting something re-galvanised!
