Hi Geoff, I don't wish to be rude, But don't waste your money on one of those unless you are doing a damp repair in your van that fine, But just to use it for the winter to keep the damp out your electric bill will be high !!
All the years we been caravaning every winter we put two plastic tub fill the top with crystal so they can collect the water [damp air] one up each end of the van, and on a nice winter dry day we open the door for a while, That if you got your van in your back garden?
But if you do use one of those be carefull of dry rot if you use it too much,
Two years ago we brought big bag of crystal and that last for the two winter, much cheaper than the electic bill, What ever you do it your choice, trevor123