The term of office for the members appointed by the county board of supervisors shall be for a period of four years, and the term of office of the members appointed by the municipalities shall be for a term of three years. The method of filling vacancies shall be determined by the county board of supervisors and municipal legislative bodies, desiring representation on such commission. The members of such regional planning commission representing counties and municipalities shall receive no compensation for their services, but shall be entitled to receive their actual and necessary expenses incurred in the performance of their duties.