Up-here in quebec, most of the shops will use to different type of product specially made for rust proofing. Both are oil based, but one contain wax in it. On a newer vehicule, they have a tendancy tu use the one containing wax. It is cleaner, and will cure to a harder finish. Will need some touch -up every year for best reslut. But as the vehicule age, it will create some flexibility in frame and body, them they will start using the one w/o wax that do not crack at the flexible joint. Also need to touch up some of the more expose area.
One exemple of that product is made by Sinto racing.
http://www.sinto.ca/en/byproduct#!p=384
And our snow started in december, and should stay up-until and of april. Did you say salt, sand and light gravel on black top road??