(1) The trust fund of a joint public agency self-funded plan shall be legally liable for payment of all applicable benefits stated in the statement or schedule of benefits in effect at the time a claim thereunder arises and subject to the terms of the joint powers agreement.
(2)  Funds in the trust fund are fiduciary funds, and are not liable for any obligation of any employer participant in the plan, nor subject to garnishment or levy for the obligation of the beneficiary. This subsection (2) shall not be deemed to prohibit levy upon the trust fund by any provider thereof, or its assignee, for health care services rendered a beneficiary if the trust fund has theretofore agreed in writing to pay for the same direct to such provider.