A cargo body includes sidewalls constructed of pairs of panels secured together at respective joints. Each of the plurality of panels is a composite panel having a core, an interior skin secured to a first side of the core facing the cargo receiving volume, and an exterior skin secured to a second opposite side. Each joint includes an interior splice plate and an exterior splice plate, and co-facing edge portions of the adjacent pair of panels are sandwiched between the interior and exterior splice places. Each edge portion defines a region of reduced core thickness in which a core thickness measured between the respective interior and exterior skins is less than a maximum core thickness. A recess is formed by the pair of interior or exterior skins to receive the corresponding splice plate, such that the corresponding one of the interior and exterior splice plate is nested into the recess.