I may be late to this, but my previous research on RC mentioned that people were using marine paint, which I wish I used:
"The Duralux 1-qt. Sub-Trop Red Primer is high quality rust inhibiting primer for iron, steel or partially rusted galvanized surfaces. Recommended for use in light to moderate marine exposures where good chemical, corrosion and salt water resistance is required. Sub-Trop Red Primer is chromate free, using safe but highly effective rust inhibiting pigments that emulate the application properties and surface protection afforded by traditional red lead metal primers."