I have had my Mizuno gunmetal wedges for 3 years & played extensively with them. Basically not a sign of rust althoug they display that nice "I've been around" patina. They got a bit rusty ONCE when I left the clubs wet in a confined space (bag with cover on) for some time. Wiped them with a wet cloth and they got the finish back. Minus the rust.
Guess its a matter of climate - to some extent. I mean cars Hawaii that are not kept indoors at night get rusty roofs(!).
I don't see a problem. Except if you live in Hawaii and leave the clubs in the garden for a while.
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)