One thing that I believe is better than anything here in the rust belt to keep your car from rusting is to keep it clean. Not just the outside of the body--the underside as well. I run my daily drivers through a car wash that also does the underside about once a week in the winter. I have a 2000 Grand Caravan and the underside looks almost new. My dad never washed his (also a 2000) and the underside was so rusty it was almost unbelievable. He needed to replace his brake lines, rear heat tubes, part of the fuel lines and a gas tank strap. All of mine aren't even rusty.
Keeping the drain holes open is very necessary as well. My first car (1964 GTO) had the rocker panels full of water when I bought it (1975) and when I drained them out it looked like someone filled them with top soil. Fortunately the rockers on those cars were galvanized. (the only part in those days)