30 pint dehumidifier enough for travel trailer?

all I know is that last spring, before i knew any better, we had the furnance on at night when it was around 35 degrees outside and no windows or vents open and when we woke up all the corners in the camper were wet.. I thaught we had a leak(camper is one years old).. the following night we opened the window and the vent and it was dry ever since..... but like i said, gets cold as heck with the window and vent running...