Water traps

Give it time and they’ll collect water. They’re bound to as they’ll draw damp in from the big outside.

We use them and yes the crystals go in the top bit. We use a small fan heater in the caravan when not using it but only set to frost. We've had them in since end November and took them out about a week ago. Barely a centimetre of water. Caravan was dry when we went in. We left the container in the kitchen in the house in error and after 2 days it was nearly full.

I remain dubious about the benifits. We did use them the first year we had a van but did not bother thereafter. As a caravan is not a sealed environment surely damp laden air is just replaced from outside. So in my case I would be trying to dehumidify Nottinghamshire. I think the main thing is to put the van into storage during winter weather, in a dry a condition as possible. So for instance not using the shower on the last day.

Never used heating or dehumidifiers in over twenty years of owning motorhomes/caravans the only issue we`ve had is when using a cover one winter resulting in internal mildew spots. Keep cupboards etc part open stand cushions to maximise air circulation and that's it.