My P5 pkg car is notorious for the windows to fog over when ever it rains or sudden drops in temps. A simple way to keep the windows from fogging over is to clean the inside of the window with shaving cream. I cleaned my windows, with this technique ,this morning and drove through rain, sleet and snow-( and yes, even the dark of night)- and I never had to wipe the inside of my windows to see. This trick also works to keep the bathroom mirror from fogging over. Try it out for yourselves. Simple, effective and cheap.