LISTENERS who propose spending all, or even part, of their holiday this year camping, will find some valuable advice in this talk by Mrs. Dawson Scott , founder of the P.E.N. Club and authoress of many novels. Mrs. Dawson Scott invariably spends a part of each summer camping in Cornwall (a county that has been the scene of some of her best novels, including They Green Stones'), and will have some very practical hints to give.on this cheap and excellent way of spending a summer holiday.