If you've ever tried to wash a down item in a tub of water, it's actually pretty hard to get it soaking wet.

Ventilation isn't about wind, exactly. It sounds like your campsite is in an area that sets you up for the condensation.

I would get a driducks poncho and drape it over the bag.
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com