Abstract: A generally horizontal load bed construction including upstanding opposite side walls is provided together with an elongated flexible cover for extension and retraction over the upper edges of the side walls of the load bed. One end of the load bed is provided with a winding member to which one end of the flexible cover is secured for winding thereon and the opposite side walls of the load bed include elongated generally horizontal tracks extending longitudinally thereof and including downwardly directed opposite end portions. A pair of upstanding support arms are secured at their upper ends to the extendible and retractable end of the cover and the lower end of each support arm includes a pair of follower members spaced on opposite sides of the support arm and engaged with longitudinally spaced portions of the corresponding track or track member.