Improved trailers (e.g., semi-trailers) are disclosed. The trailers may include a floor having a top surface and a bottom surface, where the top surface is adapted to transport a payload, and an elongated shell connected to the bottom surface of the floor, where the elongated shell defines a portion of a substantially closed torsion-resistant chamber of the trailer. The trailers may have a torsion resistance that is substantially higher than conventional trailers of similar size and/or load capacity. The trailers may weigh substantially less than conventional trailers of similar size and/or load capacity. The trailers may realize a bending resistance that is at least equivalent to the bending resistance of conventional trailers of similar size and/or load capacity.