I discovered a product called “Rust Bullet” about a year and a half ago, and it’s absolutely amazing. I had purchased used sheet metal to replace the tank and fenders on a new ’03 Harley. I thought I liked the Centennial paint until I saw a million of them on the road—I had to have something different, you know? Then I found that the inside of the freshly painted tank had rust in spots I couldn’t see.
I painted a few rusty items, like washers and a rusty wrench, and this stuff becomes impenetrable once it sets. It’s even used inside tank ships, where rust often resembles bark more than actual rust.
Check out their website, rustbullet.com, for more details. It’s not cheap, but it holds up even inside a gas tank.
WMM