It might be a good idea to look at websites of dealers to start with to get an idea of what you would get from them for £5000. Then you could look for private adverts if you would prefer to stay away from dealers.
without being rude,how longs a piece of string,the same goes for caravans,some are good some are bad in every make of van.the best i can say is take a damp meter with you and use it in every corner before you buy....see Buying Secondhand
------------- the only silly question is the one you do not ask.