I've used RIG to safely store the guns I never shoot. But there's several heavy greases you could probably use without paying extra for "gun" grease. You can pick RIG up at many gunshops or at www.brownells.com

You'll notice you don't see grease or oil on museum weapons. They use a wax. Here's an interesting article.
http://nra.nationalfirearms.museum/c...nservation.asp