yes he is as long as no one lives in it, as for the light matter, there is no a law now to say you have to have natural light, even if you did have it in the first place.
hope this answers your question.
but some estates have covenants stating things like no commercial vehicles, or vehicles of certain descriptions. i imagine caravan might fall into such a category. a mate recently went so far down the route of buying a house, paying a certain amount of legal fees etc, only to find out he would not have been able to bring home his work vehicle (his only means of transport).