I've been using a synthetic gun oil called G96...the aerosol. You wouldn't think gun rust in AZ is an issue but it is, especially if you are sweating on it or when the monsoon humidity goes from 2% up to 50% in a day.
My friend introduced me to G96. He started using it in Florida. Said he would pack up guns for the range and, even if he didn't shoot them, by the time he got home they would've started to get surface rust. He started with the G96, followed the instructions on the can, hasn't had rusting issues since.
Me either.
Jon