I think what you want to do is a version of Stuntbusters AeroJeep.
http://ecomodder.com/forum/showthrea...eep-21160.html
It looks reasonable to live with. Also your Boat tail will be shorter than your picture. Since your car is taller than it is wide, you'll end up with a Fishtail that'll terminate before the top and bottom are able to reach each other.