In the discretion of the Authority, any bonds issued under the provisions of this act may be secured by a trust agreement by and between the Authority and a corporate trustee, which may be any trust company or bank having the power of a trust company within or without the Commonwealth of Virginia. Such trust agreement or the resolution providing for the issuance of such bonds may pledge or assign the fees and other revenues to be received, but shall not convey or mortgage the airports or any part thereof. Such trust agreement or resolution providing for the issuance of such bonds may contain such provisions for protecting and enforcing the rights and remedies of the bondholders as may be reasonable and proper and not in violation of law, including covenants setting forth the duties of the Authority in relation to the acquisition of property and the construction, improvement, maintenance, repair, operation and insurance of the airports, the rates or fees or other charges to be charged, and the custody, safeguarding and application of all moneys. It shall be lawful for any bank or trust company incorporated under the laws of the Commonwealth of Virginia which may act as depositary of the proceeds of bonds or of revenues to furnish such indemnifying bonds or to pledge such securities as may be required by the Authority. Any such trust agreement may set forth the rights and remedies of the bondholders. In addition to the foregoing, any such trust agreement or resolution may contain such other provisions as the Authority may deem reasonable and proper for the security of the bondholders. All expenses incurred in carrying out the provisions of such trust agreement or resolution may be treated as a part of the cost of the operation of the airports.