The higher the humidity, the greater the frequency of inspection for rust.
Remove all furniture and store separately.
All metal parts (inside and out) especially the bore, chamber, and breech face should get a coating of grease. RIG is great, but many have used simple brake bearing grease with excellent results. The idea, again, is to completely cover all metal parts.
Place into a heavy plastic bag and vacuum seal.
Another idea (heavier, more expensive, harder to inspect, but a better method if you are looking for LONG term storage) is to get a length of PVC pipe that allows the rifle to fit inside, cement on 1 endcap, place in metal piece/pieces, fill with grease (heat it enough to flow) and thread (or cement) another end cap.
Think Han Solo encased in carbonite. Excellent method if you want to forget about inspecting for a dozen or more years. The metal will be extremely well protected. This method may need the additional step of drilling a hole in the final endcap to allow an equalization of pressures and finally sealing that hole.
Finally, dont forget that even if mags are plastic, floorplates and/or springs are metal.
