An assembly for closing an opening comprising a door panel adapted for sliding movement between an open position and a closed position, a first extendable member located at a first edge of the opening and extendable towards an opposed second edge of the opening, and a second extendable member located at the second edge of the opening and extendable towards the first edge of the opening, and wherein the door panel includes a stop member attached thereto and movable therewith, the location of the stop member defining the limit of movement of the first extendable member towards the second edge of the opening, and the limit of movement of the second extendable member towards the first edge of the opening.