FYI, the Merc ducting to the tail light was very similar (though more subtle) to the ducting modification in the PDF link, above.
As for tapering the bodywork, glad you're thinking curves rather than just angles.
15 degrees in 6-8 inches seems like it may be too much, too soon. FYI, attached flow at 22 degrees is only achievable as the ultimate angle/tangent in the curve for a given shape. If you get to 22 degrees (or any angle) "too soon", separation occurs.
Have you seen this thread?
http://ecomodder.com/forum/showthrea...rt-c-9287.html
PS - congrats on the fuel economy improvement so far!