I am a great fan of dehumidifiers in the home. We bought one for our new build home a couple of years ago to draw the moisture out of the building fabric and use it extensively for drying clothes over the winter.
It really is a wonderful piece of kit when you are dealing with an enclosed environment where you have closed off the entry of fresh air, but that is not the case with your Eriba.
Your van has air vents in the floor and one in the roof. If you used a dehumidifier, one specifically designed for the lower outside temperatures and not a domestic model, you would be trying to dry out the county. You would need to be constantly emptying the thing or have an overflow pipe through the floor. I do not believe a dehumidifier will contribute to damp issues, but it will certainly not help matters.
The general consensus of the majority of owners is to get your bedding out of the van and into the house. This acts like a big sponge that holds moisture. Next get the seats/mattress away from the sides of the van, open up all cupboards, lockers and doors etc and you should be fine.

And in case you are wondering, do not bother with a small heater. If you did manage to raise the temperature on the days where temperatures drop to freezing you would be just increasing the potential damp problem. Warm air holds more moisture than cold air and condensation would be more likely.

Colin.

I'm not necessarily with Colin on the home use but my experience with buildings is normally the design and construction of new buildings with lots of glass. In that enviroment we found that the benefits of a dehumidifier were only short term while all the water used in the construction of the building dried out. Beyond that there appeared to be no further benefit because of the glasswork.

Fully agree with Colin's comments regarding Eribas and other caravans or even all outdoor temporary buildings. Unless hermetically sealed you'll be replacing the "treated" interior damp air with another load from outside, second by second.

Randa