Check your fan speed setting. If it is set to "Auto" and your temp setting is within four degrees of the temp in your trailer, then the fan is running at low speed and may not push enough air through the heat exchanger to keep it from freezing. The only way to change the speed is to select the fan mode and change the speed to medium or high speed. This will move more air, but is also louder inside the trailer. You may need to do this on days with fairly high humidity levels.
Dale & Carol
2010 CF30SK Patriot