I lived in chicago many years before moving south and found that frequent washing at car washes will hasten the rust problem. Most car washes merely filter the water used due to the expense of high water bills so the salt from every other car gets into the water you are spraying on your vehicle. Also, the salt water brew you are spraying will get into every space of your vehicle that normal driving would not such as inside doors, under the hood ect. Very few car wash locations use fresh water but they do exist. They advertise the fact that they use only fresh water and they are very expensive by comparison. To prevent rust you would need to follow the advice given about the oil treatments and stay away from regular car wash facilities. Sorry to say, the road salt will still cause you problems but you can slow down the process.