elec problem, alternator? Starter? Help please?

Hi, got T4 caravelle camper, petrol engine out of 6 months sleep no probs, had RAC confirm that both engine battery & leisure were charging well via atuo relay. Had 4 days touring Suffolk no problems, drove home approx 2 hour drive, parked to unload, went to take to storage yard and wouldn't start? Left if a couple of hours and it started? Any ideas what is the problem...