Salt does more than just attract moisture. Live in a beach house for a year and I guarantee your brand new car will be a rust bucket at the end of that year.
Kalawang
Yeah, I don't really think salt "attracting moisture" is really a significant part of the problem.
Salt water is a much better ectrolyte than plain ol' rain water. It conducts those ions better and makes the oxidation happen faster.
I religiously wash my truck regularly in the winter around here.
I don't know if it actually makes a difference, but after washing off the salt and grime, I use the "spot free rinse." On the underside.
I assume the spot-free rinse is just softened water, and I'm fantasizing that it might be better at dissolving the salt, and will leave a less-electrolytic coating of water when I drive away from the car wash still wet.
Odds are good that I'm totally off on this

Hayes