heaters (If that is what you have running) will contribute greatly to the condensation. Catalytic ones are the worst. I have a furnace
now, and still get a little.
2. Ventilation will help reduce it. Leave a window cracked, and the roof vent open a bit, if not all the way. I know, this makes for heat loss, but ventilation, above everything else, will help the most.
3. Put "Heavy" curtains on the windows
. I actually had vinyl ones in my 13, and that helped a ton as an insulator between the cold air at the windows and the cabin. (The windows had condensation, for sure, but it didn't "Leak" into the cabin as much)