what you need to remember with the fun cup cars is that theres a rad in the front of the car, heance the big vents in the valance and bonnet.
not sure how well they would work as the as the splitter/side planes look like they would be a very turbulant area.
the quattro above is the way i was thinking for my 03 race car but with a slightly more rounded wing to suit the shape of the bug. will have a splitter on rather than the lip that the rally cars had. been playing with drawings on a bug and its just working out how to do the back end to match in with the differnat front end.