Abstract: A track and trolley assembly for use with a tarpaulin enclosing system on a flat bed trailer comprises a plurality of trollies for operatively supporting the tarpaulin enclosing system, each trolley having a frame member, at least one weight-bearing roller mounted on the frame member for rotation about a substantially horizontal axis and at least one stabilizing roller mounted on the frame member for rotation about a substantially vertical axis. An elongate track has a length, a substantially vertical trailer mounting face, a substantially horizontal weight-bearing roller receiving surface disposed along the length of the elongate track means, and at least one substantially vertical stabilizing roller receiving surface disposed along the length of the elongate track.