http://www.pagendarm.de/trapp/progra...les/NACA4.html
this site has an enteractive program which changes the shape of the airfoils. I moved the sliders until i got a shape that i could fit a large rectangle inside of. then downloaded the x&y coordinates and multiple both columns by the same number to the size of a truck in feet without going over legal road width. don't know the effects of my assumption on drag. I do see where the flow is going to stay against the surface a lot longer at slower speed. what do you think about the above site. the attachment in post # 46 would be the top view with the rectangle vehicle inside. along the bottom i would have a splitter all the way around. the sides would come straight up a couple feet with this profile then just rotate the curve over the vehicle like a jump rope to form the top. the biggest drag may be the joint effect at the ground, and lots of wetted area but if I am staring with a Cd of 0.02 or such wild number how could it not be extremely low, until the engine and driver overheat of course.