Section 2. The principal office of the board shall be in Boston but said board may sit at any place within the commonwealth. The time and place of its meetings shall be prescribed by the chairman, and the chairman shall assign all members for the hearings held outside of Boston on a rotating basis, taking into consideration the expertise, qualifications, travel involved and needs of the entire board when determining the rotation. The county commissioners shall provide the board with suitable rooms in courthouses or other buildings when necessary for hearings outside the city of Boston. Adequate offices and a hearing room in the state house or elsewhere in said city shall be provided for the board.