When I lived in Detroit I knew a guy who mixed STP and kerosene and used tubes and whatnot to spray that concoction into all the hidden areas of his cars as a rustproofing much like the rustproofing services of today.
What happens is that the kerosene evaporates leaving a film of STP on everything. Despite the horrible road conditions because of the amount of salt used to deal with the snow and ice, his cars were completely rust free.
Now mind you, he didn't use this on the exterior of the car only hidden areas inside pillars, fenders, doors, etc. And this in addition to the undercoating that was a common option in those days.
