Quit trying to have sex in your car, take a blanket!!
Fog is usually a moisture/temp differential. take a paper towel and see if there is water gathering anywhere else, under seats,under floor matsback window area..... Check under your convertible top where it goes down into the boot thingy also. Do you keep your car stored outside? Moisture might be in your air ducts also. It might be climate also. I second the scotch guard on the top idea!!