I tried VHT on my headers a few years ago and it only lasted about a week before they turned to rust.

Last time I used Seymour hi-temp "cast-blast" and it holds up a lot better but still not perfect. They smoked the first few starts but after a few heat cycles it cured ok. I did them about a year ago now and they are just starting to rust again on the bottom of the car from road spray but it's easy to touch up.