i have the same exact problem as you meng, i get fog and it even gets stinky. freezes up my floormat nice and good in the winter too
ill let you know if i get anything that cures it, as it bothers me too. good luck to you

- 98 SVT #5999 -. -CDA-7894 w/ ipod interface -Knauberized, Trubendz 2.5/highflow cat