my RMS Hooptie van, (extended G20 chevy) has that problem. when i open the rear windows,or when i take the window out completly to haul lumber longer than 14 feet, i get alot of exhaust fumes, so i gotta keep em closed. not saying that my van is as airodynamic as the vx, but the fumes do linger back there, and opening the front windows dosent help that much either, seems to draw them in even more.
seems that the fumes would just blow away, but they dont.......
just makin a point..