Each port district shall adopt a resolution (which may be amended from time to time) which shall establish the basic rules and regulations governing methods and amount of reimbursement payable to such port officials and employees for travel and other business expenses incurred on behalf of the district. The resolution shall, among other things, establish procedures for approving such expenses; set forth the method of authorizing the direct purchase of transportation; the form of the voucher; and requirements governing the use of credit cards issued in the name of the port district. Such regulations may provide for payment of per diem in lieu of actual expenses when travel requires overnight lodging: PROVIDED, That in all cases any per diem payment shall not exceed the United States general service administration's per diem rates. The state auditor shall, as provided by general law, cooperate with the port district in establishing adequate procedures for regulating and auditing the reimbursement of all such expenses.