I've never had any rust problems with my two steel frames. They are relatively new (2003 and 2004), but both have been ridden in the rain at least a few times and many > 2000 miles overall, and I live in very humid central NC. I really wouldn't worry about rust - it's just not a consideration unless you get a bad scrape on the frame, in which case you need to touch it up with paint so it won't rust, of course. I don't do any fancy protection to my frames either, just clean ''em after they get grubby enough.
I love my steel frames, but they are heavier than my carbon frame. Nice for touring, on the trainer, and for rainy-day rides, though!
Emily in NC
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow