I use my leaf blower to get the excess water off my car after I wash it. I pay special attention to that area around the bottom of the doors and so far KOW I have seen no rust. My car is garage kept so it doesn't sit out in the rain except when I'm at work. I also towel dry what water is left on the car and again pay special attention to that area making sure there is no water left there. I wash my car once a week and have had no rust issues. That said nothing is fool proof.
Pat