Had this problem on a boat with a steel cabin. Warn damp air coming into contact with cold metal or windows. Result drips, not pleasant in the middle of the night.
Insulate, use cardboard as a stopgap,ideally have it sprayed with some insulating foam, preferably something non toxic, if such a product exists. you could Skin the inside in such a way that you can push the insulation in with a stick, then use warmcel insulation made from recycled paper which is also fire retardant, and harmless, or shredded paper treated with borax solution, which I believe is the basis of the flame retardant in warmcel insulation,
Drive somewhere warm.