Prior to painting, you need to wire brush down to bare metal, wash with alcohol, and then preheat the metal until it's dry with a propane torch or heat gun-you will know by watching the condensation form then disappear on the metal. This method has worked great for me on everything from brake drums to exhaust parts.
Yes, the rear drums on my truck are still black and rush-free using BBQ paint and it has been 2 years. It really makes you smile when you check the rear brakes and the drum isn't crusty
