First of all don't put a cover on the van for Winter, use the van, that's what it's for LOL. If you must lay it up , are you going to SORN it and save the tax? make sure all water is drained out of the water system, the method varies from van to van, If you have a water boiler this must also be drained, [ leave taps open , you may need to pull a
fuse to prevent your water pump from operating, dependant on your vans system, don't forget the shower tap too] .it may have an automatic valve [ the boiler ] that opens and dumps the water at a low temperature to prevent freezing check this out,any clothes and soft furnishings may get Mouldy over winter so be aware of this , Batteries can go flat especially if you have an active alarm using power,so keep an eye on this,Vermin IE Mice like a warm van in the Winter so watch out for them moving in. Try and run the Engine up to temperature as often as you can to keep the oil circulated so the cylinders don't get rusty,leave the Fridge door open to prevent smells and make sure all fresh food is removed from the van .Your water pump is at risk from freezing too so make sure it is also drained [ domestic water ]Have fun Malc.