How do you keep a caravan camper damp free?

If it is possible to store it near where there is electrical service, place a 75>100 Watt light bulb inside the vehicle and leave it lit (AWAY FROM ANYTHING FLAMMABLE OR THAT CAN MELT) during the worst periods of moist weather, and open the camper and air it out as much as possible.

If this option is not available, there is aproduct sold (in the US, anyway) by the tradename of 'Damp-Rid' which absorbs moisture from the air, but must be emptied and replaced every so often.