A cover includes multiple panels pivotally connected together and foldable between a stacked arrangement and a deployed arrangement. Side rails are attachable to opposite sides of the cargo box and include ledges. Storage extension guides intersects the ledges. The panels are supportable upon the ledges in the deployed arrangement to cover the cargo box. The stack is supportable upon the first and second ledges in an intermediate position adjacent the storage extension guides. The stack is movable along the guides between the intermediate position and a storage position in which the forward edge of the lowermost panel is oriented below the rear edge of the lowermost panel.