IMHO - cleaning is the most important step in rust prevention. I use a mix of automotive anti-freeze & water for cleaning. Wet patches & pump water in & out of the bore, then bronze brush, then more patches until they come out clean. Then I use compressed air to blow the moisture out of the bore. Then a good thorough soaking with WD-40, set a minute then blow that out with compressed air. A couple clean dry patches, then a good coat of a quality gun oil (I like Rem-Oil). On my hooked breech sidelock I also use a small bronze brush that fits on the end of the ramrod to clean the breech plug face during the cleaning.
Using this method I've had no rust problems at all!