Hello Micheal, Most of teh mainstream manufactures were beginig to use bonded wall construction, otherwise expanded polystyrene panels were still common. teh dangersof asbestos were known at that time so I think it is unlkely to find any in the wall cavity. However if you are in any doubt, seek the help of the environmental officer at your council who will be able to more specific advice, and may be able to check the caravan for you.