How can I protect my guns in storage against rust?

Mike says: A thorough clean, followed by a wipe-down of the metal parts with a lightly-oiled cloth should be quite sufficient for guns in storage, providing your friend is going to examine your guns reasonably frequently.

If the guns have chromed bores – and most modern guns have – there’s no need to leave the tubes internally oily. If you do leave the bores oily, then make sure the guns are stored muzzle-down, otherwise oil could run back through the firing-pin holes, and possibly dry out and gum up the mechanism and, at worst, soften the wood at the head of the stock.

If you wish to take a real belt-and-braces approach, the metal parts of the guns can be coated with grease, but I don’t think that is necessary in your case.