When I was tent shopping long ago, someone told me that no matter what time of year - you had to keep windows open. This is to allow air to flow. He said a single person can breath out the equavalent of something like a gallon of water per night. If you close your tent up tight - it's got no where to go. Even worse if you have a bunch of people. So how might this work in a PUP? Do the roof AC units circulate air (and exhaust inside humid air to the outside in the process)? And what about the opt. heat setting on them (the "heat strip")? If that were bringing in colder outside air - it would negate itself. Is it perhaps that PUPs have larger cubic space inside vs. a tent, so this "breath humidity" isn't a concern?