Port commissioners shall receive such compensation as shall be determined and fixed by resolution of the governing body of the cities or townships or the board of supervisors of the county or counties in which the port district is located. Port commissioners, while actually engaged in the performance of their duties, outside the area of the port, shall also be paid their actual traveling expenses, both said traveling expenses and mileage to be submitted in writing to the port commission, and to be audited and approved in writing by said port commission before payment.