I have been using this stuff for many years on all my guns. It is great for the metal and the wood. It's not expensive, and as you can see, works great on furniture too! I have 2 870 express's, and a total of 36 firearms. Nary a spec of rust on any of them. They get used too!!
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053
I do from time to time loan my guns, but the people I loan them to would never consider for one second returning one of them to me in anything other than the condition in which they received it. If something happened beyond their control I know without doubt that they would replace it or pay for it.