Moisture/Humidity in rear bed area

We finally took our new TM out for its maiden voyage this past weekend, and noticed that the rear bed area felt a little humid at night. Since the AC isn't controlled with a thermostat, when it reaches the desired temp, it simply runs the fan without the compressor -- which was drawing in damp, outside air. (One of the reasons we chose the TM over a canvas pop-up or hybrid was the notion that the hard-sided TM would keep out the humidity to provide better sleeping comfort.)

We went to Wal-Mart and purchased a $50 de-humidifer to use for the second night ... it seemed to work (the sheets didn't have that awful "moist" feeling), but I'm wondering if there's a better solution.

Can a thermostat be installed to the roof AC unit so that it simply shuts off instead of drawing in outside air, just like the AC at home?

- Mark