In the discretion of the authority, any bonds, including refunding bonds, or notes issued by the authority may be secured by a trust agreement between the authority and a corporate trustee, which trustee may be any trust company within or without the state. Any such trust agreement may contain provisions as set forth in section seven of this article with respect to the resolution. All expenses incurred in carrying out the provisions of any trust agreement may be treated as a part of the costs of the operation of the hospital loan program provided for hereunder. Any such trust agreement, indenture or resolution authorizing the issuance of bonds or notes may provide the method whereby the general administrative overhead expenses of the authority shall be allocated among the several hospitals to which hospital loans have been made.