The commission provided for in Section 17-16-66 shall sit at such times and places as may be directed by the joint convention, and shall be presided over by a chair of its own selection, and each member of the commission shall receive four dollars ($4) per diem during the time of actual sitting when the Legislature is not in session, and necessary expenses, to be paid by the Comptroller’s warrant drawn upon the Treasurer, when the chair of the commission shall certify the same to the Comptroller.