I've found that POR15 is about the most durable gloss black paint that there is. Have also done Rust-O-Leum and that works pretty well, too. Having tried a variety of products however, I have found that POR15 is the strongest and prevents rust the best. Be warned however, it is super sticky and messy to work with! I wore two pairs of nitrile gloves, and still somehow got it onto my hands. Where it stayed for a week!
