are preferably hung from the roof lining 22a as shown the floor lining 25a includes a series of spaced apart t shaped members 27 thus when the air from the duct 80 reaches the floor of the container it is able to flow along the floor lining 25a into the side wall channels 42 via the spacing between the interior wall panel 40 and the floor lining 25 thence the air circulated upward in the vertical channels 42 and into the plenum 50 as described above the cross sectional view of fig8 a illustrates schematically one of the preferred embodiments of the invention in simplified form the embodiment illustrates the cargo space bounded by interior sidewalls 40 floor lining 25a and inner roof lining 22a this cargo compartment is effectively insulated from heat ingress by a surrounding layer of heat insulating foam 36 in this particular embodiment the roof lining 22a is configured to form three separate parallel longitudinally extending substantially rectangular troughs or channels the central channel is shaped and sized to form the central air duct 80 that is divided by a central septum 84 and further subdivided by septums 84a and 84b as described above the lower plate 82 of the duct 80 s supplied with a plurality of apertures 88 as previously described above along both of its longitudinally extending edges and is mechanically fastened to the roof lining 22a the other two roof channels are covered with hinged and clasped base plates 52 to form the return air plenums 50 these plenums are in fluid communication through shutter arrangement 60 with sidewall channels 42 the lower ends of the sidewall channels 42 are in fluid communication with the volume in the vicinity of the floor lining 25a of the container in an alternative embodiment.