It'll be a foam cylinder cut in half lengthwise, with the flat half of it adhered to the airdam.
Put some deflectors on the back of the tray so the wheels don't scoop mud up onto it. I guess it might help isolate that whirlwind of air kicked up by the front wheels.
I got the MPGuino hooked up, and it functions! I'm very excited about this. The only problem is I mistakenly hooked the power source to the stereo power supply, which is not always on. At least I don't have to mess with the VSS again. I'll work on that tomorrow.