I'm parking my Jeep for the winters here in Chicago. It isn't worth the hassle of dealing with rust. Too much road salt. I don't need the Jeep that badly.
But, if you must drive through road salt in the winters, washing the Jeep is the best way to prevent rust. Spend a good long while at the car wash each week. That'll do more in terms of rust than anything you can put on it now. Remember to get inside the frame.
Winter is actually pretty easy where I am. Colorado doesn't use nearly the amount of salt as the upper midwest does. In the winter, I'll swing through the self serve car wash about once a week to hose off the Jeep. It's probably cleaner in the winter than it is in the summer.