Municipal trusts are administered by a board of three elected trustees. RSA 31:22. The trustees of trust funds have custody of municpal trust funds and administer the affairs of the trust. Trustees must act in the best interest of the tursts. They have a duty to exercise due care to manage the tursts in accordane with the directives of the donor and the controlling statutes. The trustees are authorized to engage banks and brokerage firms to assist in management and investment of trust fund resources and bookkeeping.