The motor industry has tried all manner of coatings to protect vehicles against rust, with varying degrees of success. The relatively thin steel sections of car bodies mean that the ravages of water, grit and salt can soon wreak havoc on them.
Unprotected steel will always succumb to the corrosive effects of moisture.
Vehicles which don't have a separate chassis but rely on a monocoque body for their structural integrity can be destined for an early grave if not adequately rustproofed. The use of low technology surface coatings in the early years of monocoque production meant that most such cars were lucky to survive more than 10 years.
The introduction of the MoT test highlighted the problem, particularly when corrosion damage had been done around weight-bearing areas such as sills and suspension mountings. Not surprisingly, many companies sprang up during the 1960s and '70s offering a thorough rustproofing treatment, but the benefit of such products was sometimes questionable. Treating a new car might increase protection, but applying rustproofer to a used vehicle often only succeeded in masking existing corrosion and locking in already present moisture.