We discovered the band of wall touching the edge of the fixed bed mattress was condensing moisture in our 17 A. We first noticed this when winter camping at aprox.-10. Fans, windows, nothing made a difference to this band of moisture.
I realized the space under the bed was enclosed and colder than inside the trailer. We opened the access doors to help it ventilate and voila, no more condensation! I am considering a small computer fan and vents to help keep the temp constant inside.