I read a story (I think it was here years ago) that this guy would soak his revolvers. He had a 5 gallon bucket of motor oil using a clothes hanger loop it around the trigger guard. Then drop it into the oil for a day or two. After the oil bath he would remove it and let it drip dry for a week, then wipe off the outside.
Your results may very.
I just wipe then down 1-2 times a year with Breakfree. I never had problems with rust.