How does WD-40 work in a gun case as a rust preventative? I know rem oil works amazing but after a recent hunting trip to Montague Island my pistol had some severe surface rust on the barrel, slide and frame. This was after oiling and cleaning my gun before and after it was used for the duration of the trip. I was thinking of coating the inside of my pistol case with WD-40 as kinda of a passive way to fight rust.