A trailer body includes left and right bottom rails and left and right top rails all parallel to each other. A floor extends between the left and right bottom rails. A left vertical sidewall is defined between the left bottom rail and the left top rail. A right vertical sidewall is defined between the right bottom rail and the right top rail. The sidewalls are defined by a plurality of abutted extruded wall panels that extend vertically between the respective bottom and top rails. The floor is optionally defined by a plurality of abutted and interconnected one-piece extruded floor panels that extend between the left and right bottom rails. The wall and/or floor panels can include an I-beam post/cross-member defined in the extrusion profile. The panels can also define half I-beam post/cross-members so that adjacent abutted panels cooperate to define additional full I-beam post/cross-members.