I have had several shotguns in long term storage for over 3 years. I took the barrels and oiled them with a light VCI oil and put them in a gun slip in a piece of drain and sewer (lightweight PVC) pipe. I glued one end with a pipe end piece using standard pvc glue. After I added a dissicant pack, I put in one of the VCI capsules (now carried by Midway) that emit a corrosion defeating vapor and I put an end piece on the other end and used some air conditioning duct tape (the metal faced kind- you can get it at ACE) to seal it. I labeled the removable end piece with the date and piece it contained. I check one each year and there has been no rust. They are stored in a locker in my garage, subject to temp/humidity swings.
Be careful with oil/grease coming in contact with wooden stocks, for ends, etc. It will rot them out over time.