A method and apparatus are provided to reduce the overall weight of a rear differential cooling system of a motor vehicle. The apparatus includes a body panel system. That body panel system includes (a) a rear diffuser, having a front air inlet, (b) an underbody panel, overlying the rear diffuser as well as (c and d) first and second air tunnels formed between the rear diffuser and the underbody panel, and (e) a rear valance, including first and second vent openings for discharging air received from the first air tunnel. A heat exchanger is provided between the air tunnels and the vent openings. A related method for improving weight distribution and reducing overall weight of a rear differential cooling system is also provided.