Also important to make sure, if you are using a dehumidifier or desiccant that all your door seals and window rubbers, etc.. are all good, so that the vehicle is as airtight as you can get it, so your desiccant does not become saturated very quickly by sucking in moisture from outside the vehicle.
I don't bother with a dehumidifier as my van is as airtight as a sieve. So all I'm doing is drying the world.
