Abstract: An intermodal shipping container including one or more improvements such as intermediate gable posts or gable headers adapted to increase an internal width and strength of the container, wherein the gable posts or the gable headers include twin channels having at least two internal flanges welded to a gable post plate or gable header plate, one or more upper castings having an integral top rail ledge, wherein a top rail of a side wall hangs on the integral top rail ledge, “C” channel style beam main frame cross members, a one-piece continuous top plate including an integral lip connecting the top plate and a roof, one or more rear lower castings, wherein the one or more rear lower castings are an integral interlocking interface, a bolster including an integral seating and fastening surface and slots, and/or one or more nested rear corner posts subassemblies, the one or more nested rear corner posts having a notch and protrusion connection, wherein a protrusion in a lower rear casting engages with a correspond