Why cars rust
growing up in New York is no different from almost anywhere..
THIS is simply not true. I grew up in the inland NW, and for MOST of my life, Idaho did not use any sort of chemical or salt compounds on the roads. Cars in AZ and most of CA can be expected to generally outlast those cars that showed up from a great part of the wintery --salty--E coast, and other areas--such as near heavy mining--could be expected not to fare as well.
I doubt that MOST of us --when I grew up-- ever thought of washing the bottoms of our cars, except maybe those on dirty, muddy roads.
THERE ARE definately cars which were designed poorly. Early 70's Chevy pickups come to mind--there was some sort of natural cavity up in the inner/ outer fender area which was a natural trap for road splash and mud.
I doubt that 10% of the cars in my home area were undercoated, or ever had ANY special treatment--cleaning, coating, or otherwise to the bottoms of the cars.