No commissioner shall hold other public office other than notary public. Commissioners must be citizens of the United States and they must reside within the park district at the time they are appointed or file for office and while serving and within the appropriate election district if so required by sections 398.03 and 398.04. All persons appointed or elected to the office of park district commissioners shall before entering upon the discharge of their duties severally file a written acceptance and oath of office in the Office of the Secretary of State for the state of Minnesota. Commissioners shall serve without compensation but shall be allowed their actual and necessary expenses incurred in the performance of their duties. No commissioner or any person holding appointment under the corporation shall be interested directly or indirectly in any contract entered into under the provisions of this chapter. No commissioner shall be subject to any personal liability on account of any liability of the corporation.