I agree, total waste of time, Caravans aren't airtight boxes, if you dry out the air inside it is simply replaced by wet air from outside.
And it doesn't leave water in the container, it leaves either a very salty solution if salt is used, or a very corrosive sticky solution if the crystals are used - be very careful not to spill it when taking the containers out to empty them. It will burn holes in the carpet or upholstery if you spill it on them.
------------- Caz
If you can't see the light at the end of the tunnel, just keep going till you go round the bend.
Just as a PS to this,when I had my campervan, I put bowls of salt in overwinter the first year I had it and all stayed dry....
The following winter it was stored a couple of miles away and I completely forgot to put in the bowls of salt.
Early spring came and condensation (presumably from sunshine/heat to misty windows?) ran down behind the seats and they were growing with mould underneath... The previous winter all was well in the spring.
So the moisture in the air which comes in naturally from the air ducts and then condenses on the windows on warmish/sunny winter days is lessened by the use of salt or crystals.
I know you should take out all the seat cushions for the winter, but where do you put them all??
I have never put salt or any other type of crystals in the van over winter time.I leave the large central skylight on 'night vent',open the cupboards and move/stack cushions to middle of the van.Not had a problem with damp so far. Re the mould in a previous reply, we wipe down all surfaces with a dettox solution to make sure everything is clean and smelling fresh,Oh and leave the fridge door wedged open too.
If you want to dry your air in your van out, salt or silica crystals should work perfectly well.
But, make sure you block the vents or it won't do a scrap of good. As other posters have said, the fresh air blowing in will just bring in more moisture.
The corrosive effect of salt is caused by the wind physically picking up water droplets with salt on them, and depositing them in a layer all over cars etc. Unless there is a gale inside your caravan, you are unlikely to suffer from this problem.
Theoretically, if you seal off the vents and put enough salt to soak up all the moisture in the air, this should render your caravan dry and damp free (assuming no leaks). However, the moment you open the door to empty the bowls, you immediately undo all that good by letting in moist air again.
My advice would be (if you can be bothered) to seal up all the vents, put in enough salt to easily absorb ALL the moisture in the air (probably a few pounds in 4-5 bowls) and don't go in until spring.
try b&q they have a quite large moisture absorbing kit which includes a plastic trap and a large tablet about 5 inches in diameter for under a tenner you can get refills for about 6 quid also they are called moisture absorbent traps worked for me last year
altough, to be fair, one of the huge advantages of folding campers is not having to worry whether your £20k dream van is going to turn into so much rotten mush within 3 years... Folding campers don't get the damp!
racletcharlie - mine did - thanks to snow followed by warm weather last year! We ended up with wet canvas with our Conway Cruiser Luckily we opened our cruiser up and noticed the wet canvas and allowed it to dry out. Had we left it packed away it would probably have ended up with mildew and holes in the canvas. BTW we also used an official 'all weather' outdoor cover, and made sure the camper could not capture water on its rain cover (nose up and stuff under transit cover to stop water 'pooling' on the top). We were probably unlucky, but it seems it pays to open your camper up on dry days in the winter to make sure the canvas is not wet/damp.
------------- Why am i doing this instead of camping??!!
it pays to open your camper up on dry days in the winter to make sure the canvas is not wet/damp.
Yes it does, I always did that with all the Conways and Combi Camps I've had.
When we first had a caravan (17 years ago) I used to put the moisture absorbing crystals in over the winter, but after a couple of years I realised how corrosive the "water" in them was when one of the kids spilt one, so I stopped doing it. In subsequent winters I realised that it had made no difference whatsoever to how damp (or rather NOT damp) the caravans/motorhomes got over winter.
Jax, the answer is to stand the cushions on end in the middle of the van where the condensation from the windows can't run on to them. Must admit I've never had a problem with any of the modern vans I've had, condensation on windows was a problem in the first two - glass windowed - ones we had, but only when we were using them and thus creating the moisture in the air!
------------- Caz
If you can't see the light at the end of the tunnel, just keep going till you go round the bend.
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Topic: Moisture Absorbing Crystals
Luckily we opened our cruiser up and noticed the wet canvas and allowed it to dry out. Had we left it packed away it would probably have ended up with mildew and holes in the canvas. BTW we also used an official 'all weather' outdoor cover, and made sure the camper could not capture water on its rain cover (nose up and stuff under transit cover to stop water 'pooling' on the top). We were probably unlucky, but it seems it pays to open your camper up on dry days in the winter to make sure the canvas is not wet/damp. 
