I find it always pays to be paranoid about moisture! After a shave I dry with toilet paper (including around the pins/pivot) and then strop on linen/leather. After someone else's suggestion on this forum I have put a layer of uncooked rice in the box where I store my blades and that seems to take all the moisture out of the air in the box. Outcome: in 1 year I've yet to see any signs of rust on my blades.

Water marks can, however, develop near the edge and when they get a little too unsightly I break out the Maas and a cotton bud and spend a few minutes polishing them up. (I tend to do this before I hone so it doesn't matter too much if I accidentally dull the blade during polishing.)