The lease may be made for any term not exceeding 99 years and may vest in the lessee the operation, management, development, and control of the power rights and the use, sale, and control of power produced therefrom. The lease may provide for the payment of rentals and any other matters relevant to the leasing of the power rights as the districts may in their discretion deem advisable not in conflict with the Constitution of this State nor with the express terms of the statutes under which the districts are respectively organized and exist.