i always found hammerite works a treat, nice finish aswell
If when cleaned to metal water Allow to rust repeat a few times gets the salt content out spray with an etching primer and paint will remain rust freeYeh I cocked mine up as well, the rust started coming through again after a month . Even though I cleaned them right down to the metal. Going to give it another stab soon with Fanny's suggestion.
used normal spray paint (matt black, 2.00/can) on mine, just 2 weeks ago so still looks good under the mud