I added a small 20ltr compressor style dehumidifier, few years ago. It helps, in high humidity areas, when it's not hot enough for AC. It takes couple hundred watts, so unless you have enough batteries or shore power, it just takes up room. I first tried mini dehumidifier 12vdc type. The best one, took out cup of water, in a day. Damp Rid did even less. You add pint of water, per day, per person, just breathing.
When it's cold and outside air, has low humidity, opening vent, does help a lot. When it's 40f and 80% humidity, not so much.