Remove the rust with OSPHO which will convert the rust to iron phosphate which can then be wiped off with a rag or clean steel wool. I painted my drums with black enamel paint, although black spray on bar-b-que paint would probably be better for enabling better heat transfer.
Here's some good reading on this topic, including Fordbarn.
https://www.google.com/search?q=shou...hrome&ie=UTF-8