Abstract: A hinged cover is provided for mounting on a trailer including a front end, a back end and opposite sides. The cover includes a body with a front end, a back end and opposite sides. A hinged assembly hingedly interconnects the trailer and the cover body at the front ends. The cover is movable between raised and lowered positions by a pair of jack assemblies interconnecting the trailer and the cover at their sides. The hinged assembly includes a lost motion linkage comprising a generally vertical slot into which a hinge pin is slidably received. The hinge pin slides upward in the slot as the cover is raised and downward as the cover is lowered. The cover also includes a pair of supports onto which the cover may be seated when in the raised position thereof. A pair of supports are mounted on the trailer and each includes a bifurcated upper end. The cover has a lower rim which is received in the support upper ends with the cover in its lowered position.