Do you have a busi­ness that you think would go down well at fes­ti­vals? I asked four such  entre­pre­neur­ial types, with ven­tures in T‑shirts, vin­tage tents, gourmet cof­fee and holis­tic mas­sage – about their expe­ri­ences as fes­ti­val traders. Is it a com­bi­na­tion of fun and prof­it, and are you guar­an­teed enough time out to catch a favourite band? One…