A panel has a first edge portion defining a first end of the panel, and a second edge portion defining a second end of the panel. The length of the panel is predetermined for the panel to reach across a vehicle chassis frame in an installed position in which the first edge portion rests on a side beam and the second edge portion rests on an opposite side beam. The panel further has a longitudinal rib. A first end of the rib is located adjacent to, and inboard of, the first edge portion. A second end of the rib is located adjacent to, and inboard of, the second edge portion.