Self inflicted injury! Lack of airflow to remove all the steam and hot air from the driver *grin* All the rain and snow on your clothes and those lumps of granite you put in the back need longer runs to dry the car out, or put a fan heater on an extension lead in the car with the windows slightly open and dry it out every few weeks.
On the decent runs thingy. I used to motor down to Bath, a run of about 400 miles, but I now take the train. Less hastle/stress and cheaper. I don't remember that the Condensation problem was noticeably alleviated, but it may have been.
That's why you have a condensation problem. It's sitting with the windows closed, and it's full of moist air which doesn't move much. As the temperature outside drops the moisture condenses on the windows.