condensation

It depends on the climate your coach is in. If we are traveling to a cool or cold wet climate area i.e. a place with very high external ambient humidity then the dehumidifier runs constantly. This was especially true when we got caught in a bad snowstorm. Opening an external vent won't help much in that case because all it did was bring in cold wet air. As soon as we added the dehumidifier all the issues went away. It was a nuisance constantly dumping the dehumidifier bucket but better than having massive condensation all over the place. When we camped where it was very cold but dry such as NV we had no problems with humidity and we simply opened a vent and exhausted the warm moist air. We have camped all over the western US from AZ to WA and as far east as CO & MT. We had most of the issues in Western WA and OR particularly near the coasts when in very cold (snow or rainy) weather. Note, however all bets are off if using an internal vent free propane heater. I have direct experience with that and it will produce massive amounts of humidity and unless you have extremely low external humidity it can produce major condensation problems. At 75 degrees F the dew point is 45F i.e. if the external temperature is less than 45F and the relative humidity is greater than 35% you will get condensation.