Well how would I diagnose that there is something wrong; heater works fine, never lets in water no matter what the weather, never any wet patches on floor/doos/boot etc, dosnt return once I have the blowers on the windscreen, no homeless person sleeping in my car. the only time it does return is if I clear it with the heated front windscreen (yes, im sure it has one) then turn the heated screen off and dont have any blowers on the it comes back. If I drive with the windows open then it doesnt get wet.
Only thing I can therefore think of is that the water which is naturally in the air as a result of having 3 or 4 people in the car at times,. and the air wbeing warmer therfore has a higher dewpoint and can hold more water than the outside air, when the car is left and the air inside the car cools the water condenses onto the cold surfaces, ie my windows, becuase the air cant hold as much water.