The rig will need to have it's own primary insurance even if the renter has coverage from their own agent/policies. Not many companies will provide coverage for an RV that is rented and the policies will specifically exclude coverage if rented. You would have to establish a business (maybe an LLC would work) and then title the RV in the name of the business (relieves you of personal liability). You then should seek out an insurance broker to obtain coverage for your business. Your business operation-- RV rental company.