Forget about oiling it. In a short time oil will move, leaving the steel susceptible to rust again. IMO, your best bet is to use RIG (Rust Inhibiting Grease), made by Birchwood Casey and sold by Brownell's and others. It contains calcium sulfonate and is the best rust preventative you can put on you guns. With RIG in the barrel and chamber and on the exterior, I've stored guns for years without a spot of rust on any of them.
An old piece of T shirt impregnated with RIG and wiped over the guns after handling and before putting them in the rack will insure that they'll be free of rust. I've used this method for over 40 years.