We have found that the absolutely best thing is a microcrystalline wax, sold to museums and to furniture restorers as Renaissance Wax. Happich Simichrome is useful for removing light
rust and cleaning the metal prior to the waxing (motorcycle shops often have it). Keep all pieces separated in their own bags (pillowcases work well), since scratching wears pieces more definitely than does moisture. Lastly, polish from time to time bringing the polish back up to a high gloss using a buffing wheel and greaseless compound.