The trustees may contract only with the county to provide road services including road paving, reconstruction, or maintenance, according to the county’s standards for such services, on roads within the district and on any road outside the district that provides a direct route between the subdivision comprising the district and the nearest paved street or highway, other than roads identified under section 357I.2, subsection 3, and may certify for levy an annual tax as provided in section 357I.8. The trustees may purchase materials incidental to the administrative functions of the trustees and perform all other acts necessary to properly maintain and operate the district. The trustees are allowed necessary expenses in the discharge of their duties, but they shall not receive a salary.