Hi Nick,
Its a good idea to get your caravan off its tyres if you do not intend using your van during the winter. I do not think that axle stands are such a good idea. They are ok for temporary use but they do not realy provide the stability for long use, a high wind could easily move and topple your van. I use winter wheels, these offer stability plus security as they have a security lock. I bought mine from Towsure but many caravan shops sell them.
Good luck.
JTS.