A trailer includes a pair of vertical, spaced apart opposing sidewalls and a roof sheet extending between and mounted atop the sidewalls. The sidewalls and roof sheet cooperate to define a cargo space. The roof sheet has an interior surface facing the cargo space and an opposing exterior surface. A plurality of bows are mounted to the exterior surface of the roof sheet and extend between the sidewalls. The plurality of bows support the roof sheet. Each bow includes at least three contact portions attached to the exterior surface of the roof sheet. A rib portion interconnects the contact portions and defines a channel between the rib portion and the exterior surface of the roof sheet.