Since most campers are not hermetically sealed, moisture from outside will continually equalize with the inside. Remove some moisture and more will seep in.
Condensation occurs when the surfaces of the camper reaches the dewpoint of the air inside. Mold and mildew do not need condensation, just a moist (high relative humidity) environment, even if it is only a few hours each night.
Heating the inside air lowers relative humidity (keeps air temperature further above the dewpoint). Warmer air can "carry" more moisture.
I use a small tabletop dehumidifier with a timer to come on in the evening for about 8 hours. This is when temperature is lowest and relative humidity is highest.
Some of these small peltier junction dehumidifiers can also run on 12 volts with the right adapter. They have a small reservoir that needs to be dumped occasionally. They are $30-$50 and seem to last about 2-4 years. I just replaced mine.
Hope this helps,
