Definately need the steel wool and adhesion propmoter for going over chromeI've had really good luck with the Duracoat Spray Bed liner on exterior parts.A little more expensive and you need to do a thorough job of prepping the suface. Works great if you want that matte Black texure.

Don't do it. Go straight to herculiner or line-x. Little more prep but as soon as rocks hit anything that spray paint is coming off. I throw rocks at my lined bumpers, grills, side mirror covers or fuel door and they just bounce off.