closed cell foam extrusions of neoprene epdm silicone etc the cores are shown in fig4 with c clamps 24 and 26 around the ends of the cores fig5 shows a cross section of the cores 20 separated by c clamps 26 and fig8 shows a cross section of the cores 20 separated by a hollow element 27 co molded and integrated within the walls of the mold suitable for running utilities within the mold shown in fig6 are two openings co molded into the walls the larger opening 86 is suitable for a door or larger system and or equipment such as a mechanical refrigeration unit and the smaller opening 84 is suitable for a window or smaller system or equipment supporting ancillary structures can be appended to the walls of the composite box such as the metal attach plate 94 shown in fig7 in addition hollow elements 92 having endings at the surface of the walls of the composite box can be filled with a removable substance not shown such as clay to prevent the hollow openings from filling during the process of filling the molds a typical mold lay up as shown in fig9 consists of a mold 70 a film or sheet of surfacing material 72 the fabric lay up 74 a core.