As long as that powder coat is on there, you will never stop that rust creep. It will just keep holding moisture and working its way up. I have always blasted and painted them.
It's a ton more work, but I prefer to galvanize and then paint them. Takes a lot of prep however to get the galvanizing smooth so it doesn't show and get the paint to stick. Have to acid etch, epoxy prime then topcoat. PPG makes a 2 part industrial paint that is nearly bulletproof.