Condensation

You are getting condensation because there is more moisture inside the trailer than outside. Cooler air contains much less water. Short of keeping it cold inside, you have to try to Remove all sources of moisture in the trailer as much as possible. Dry dishes, dry up the shower when you’re done, don’t leave any open containers of liquid around. Actively vent the trailer when using water or cooking. That leaves your exhalations overnight as the primary source of the water. Since you probably don’t want to hold your breath all night the only way to get rid of that moisture is by having some ventilation. As jato days it’s necessary.

Try leaving the vent open and cracking a couple of windows, the warm moist air in the trailer should rise up through the vent and be replaced by cooler dryer air via the windows, without needing to have the fan on. Experiment around a bit to see what works, it will change with varying outside temp, humidity, and wind conditions.