nightrider, if the rust has been painted over 9 times out of 10 it was cleaned and scuffed before the paint so it won't get much worse over the winter since its sealed off from moisture and air pretty good, but if your really concerned just strip the panel, clean it and Por-15 it. it can't look much worse than painted rust and it will absolutly stop the rust in its tracks and forever prevent it. Then when it gets warm just get the car repainted like I'm sure you already planned to do. If you already havn't just go to the <a href="http://www.por-15.com" target="_blank">Por-15 website</a> and look over their products. If you need anymore help let me know, happy to do so.