I admire the thought you have put into this problem.
A full-bodied car, for best results, needs the whole wheel opening sealed to prevent turbulence, the enemy of good aerodynamics. Steering becomes the bugaboo.
The Ford Probe V concept car used a steered cage to contact a flexible urethane body panel to facilitate steering. Probe V had a CD of .137. There are pics in the below thread. But we don't all have the unlimited budget they have.
I studied quite a while trying to come up with something and here it is:
http://www.gassavers.org/showthread.php?t=2173
These have been on Old Reliable since November 2006, and lasted thru a full winter of snow, ice and mud. Didn't spend very much and they did the job. I am sure they are a large part of my success with this car.