Abstract: An air return bulkhead is provided for mounting on the interior surface of one upstanding wall of a container, the container wall supporting an airflow heat exchanger assembly on an upper portion thereof including a central downwardly opening air inlet, a pair of upper opposite side horizontally and oppositely outwardly opening air inlets and a central upper temperature conditioned air outlet. The bulkhead is constructed to define an upstanding return airflow path extending upwardly along the one wall with the airflow path including a central portion and a pair of opposite side portions. The upper end of the central portion of the airflow path is registered with the central downwardly opening air inlet and the upper ends of the opposite side portions of the flow path are disposed outwardly of the opposite sides of the airflow heat exchanger. A pair of opposite side upper extensions are provided for the bulkhead and mounted on the latter in adjusted upward extended positions relative thereto.