Thanks, really helpful post. The plan is to do a lot of work to the caravans and make them into a proper house. For outside we were thinking of going for an earth shelter house, so earth on 3 sides and on the top. Should make it well insulated. Sounds like planning permission shouldn't be too hard. If I build it the way I'm planning to I don't think it will be movable at all so building regulations will be an issue.