I'm pretty disgusted with hammerite, compared to what it used to be the modern stuff is c**p. I use Waxoil (black) or underbody shutz with waxoil, you need a compressor and special gun to put this on though. Don't worry about mud sticking to it, it's no worse than any other painted surface for this and it means it stays flexible so you don't have the same problems with stone chips.