We lived in a 30' 5th wheel with a super slide for one winter while the house was being built. The unit was the typical summer time camper with R7 walls..roof....floor.
Condensation was terrible. We tried the vent cracking...window cracking but all that did was make a very cold drafty camper/furnace going 24/7 with wet walls.
I finally bought a dehumidifier which helped but not enough capacity. Bought another and no more wet walls.
That was in the mid '90 and I don't remember brands or sizes but we think they came from a Lowes.