There's one other possible source for extra water vapor in the cabin that I've had happen on a Saab. I noticed a similar situation, along with a slight coolant smell--turned out there was a small leak in the heater core! Once that was fixed the foggy windows and the odor both had vanished.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)