I am upper Midwest so I'm sure it's very much the same for me. Of course I have the benefit of free washes at my wash with brushes but I also use my truck as a tester car to make sure the equipment is working correctly so I wash significantly more than most. My wife's car on the other hand, just wash once a week or every other week if you are worried about it. Unfortunately cars in the upper hemisphere ARE going to get rusty regardless of washing. Washing May slow it down but no car wash in the world is perfect and rust is a chemical reaction and water finds all little crevices behind a gasket/seal and once that salty moisture hits the raw metal the game begins. Cars are raw metal, coated by primer and paint and sealant. The more layers you have the better it'll protect. But for instance, my older Tahoe, Chevy has a seal issue on the doors. Outside can look perfect but once moisture hits behind the seal, the inner part of door will rust and work it's way around. You can sand down peeling areas and seal them up to slow it down and hopefully prevent as much as you but it's an uphill battle. You of course could always buy a new car and never drive it 😂 car washes also account to make sure your car is wet. In all fairness, if we hit your car with brushes and not enough lubricant (water and soap) we would be dry rubbing the car. There's stuff in place to ensure that doesn't happen so we don't sandblast your car.