I found a link for you that has some helpful info.
http://www.garagejournal.com/forum/s...ad.php?t=77132
With the humidity we have had lately here in Texas I would look into the products suggested in the link.
20+ years ago I started to make a small tool maker's vise out of a chunk of steel. I surface ground the base and jaws then sprayed them with a LPS product, wrapped them in a red rag and put them in my tool box. About 5 years ago I found the forgotten vise and unwrapped it. To my surprise it only had a small amount of surface rust on the edges of the base. There are some good products out there for this application.