In the discretion of the legislative body, such bonds may be secured by a trust indenture between the municipality and a corporate trustee, which may be any trust company or bank having the powers of a trust company in the state, but no such trust indenture shall convey or mortgage the system or any part thereof. Such indenture may contain reasonable and adequate provisions for protecting and enforcing the rights and remedies of the bondholders and may restrict their individual rights of action as is customary in trust indentures securing bonds and debentures of corporations.