A trailer box, comprising: a front wall, a back wall, a bottom wall, a top wall interconnected at 90 degree angles with a tubular metal frame comprising a plurality of structurally interconnected frame sections to form a hollow inner rectangular or trapezoidal portion and with opposed end portions comprising one or two hinged openings, wherein the plurality of structurally interconnected frame sections comprise four long horizontal frame sections, at least four vertical frame sections, and at least four horizontal frame sections providing a rectangular or trapezoidal frame, wherein the plurality of structurally interconnected frame sections comprise a metal selected from the group consisting of steel and aluminum, and wherein the trailer box is mounted on an underside of the trailer to provide storage for hauling 4×4 posts and/or dunnage.