I dealt with this in my 13 footer. (I oddly don't have much of a problem with the 17, but it has more air in it
Two dogs make it worse, trust me.
I put very heavy "curtains" on the windows
(Actually, rag rugs) and that helped quite a bit. You could cut reflectix to cover the windows
at nite. Cutting the cold to warm air factor definitely helps. The windows have the biggest hit for this.. ice cold outside, toasty warm in... makings of an indoor rain shower in the works!
Using a propane
cat heater was a problem, if the humidity outside was high. Heat and humid didn't seem to make a difference for me. Humid.. is humid.
Try to toss out the trash at nite if you have wet paper towels or stuff. I also put my bath towels in the car.. anything that held moisture made it worse.
I used a foam material used to seal sills in construction around the perimeter of the cushions.. in between the cushions and the walls. This gave the moisture a barrier from getting the cushions wet, and with Normal" condensation, I had dry bedding. In heavy stuff, the water would simply run down and get caught near the lower edges.
The smooth walls collect it, and I image any model with no rat fur or ensolite stuff have this issue, or.. at least, it seems worse because it is right there in front of you.