I see a lot of trucks with body rust around the rear wheels, and a lot of cars with body rust behind the front wheels and below the doors.
I've been looking into trying to repair some rust on my car and the rust converters I've looked at recommend sanding down to bare metal before applying the rust converter. If you can apply it to non-rusted steel, why don't car manufacturers treat these parts of the car with rust converter at the factory to make them more corrosion-resistant? Or do they perform some sort of treatment and it simply cannot stand up to roads that are salted in the winter?