People and pets breath out a surprising amount of water vapor. When the warm moist air hits a cooler surface the air becomes denser and can no longer hold the moisture and water forms on the cool surface. So you either need to let the air change with the outside air or have some other means of getting the water out of the air. If you are running an A/C or a properly vented heater you should have no problem. On nights when you need neither you should vent your camper. Open a window close to your head just a few inches. A Fan stirring the air also helps but without ventilation it cannot prevent it when conditions are right.