An apparatus is provided including first and second base members having upper and lower flanges, and a cover. The second based member is configured to be adjustably attached to the first base member to define an opening. The cover is configured to be attached to the first base member and/or the second base member to cover the opening. The upper and lower flanges of the first base member are configured to receive a first edge of a hole of an air conditioner plenum and the upper and lower flanges of the second base member are configured to receive a second edge of the hole of the air conditioner plenum.