If you loose cooling water , the moisty air proberbly come´s from there. Even a very small amount of coling water will give a moisty window due to the glycol in it.
If you don´t loose coling water, it´s a drainage problem , somewhere in the flow of the heated air.
If you get heat in the car it also could come from water inside the car , check if its wet under the carpets

I have not hade this problem with my V8 , so I can´t give you an hint where to look in the airflow or where draining points are, but I have had this problem on several other cars

Bengt