Side skirt setup

[dongs]

I'm new to making aero mods and have started small for my current tank. My cavalier averaged 26.8 mpg before this tank and if my math and gas gauge are even remotely accurate I'm on track for a healthy ~10% improvement for this tank. I've kept it moderate and only removed the antenna, passenger side mirror, and blocked the vents on the bumper with packing tape.
I want to make some more changes and wheel skirts/side skirts/wheel spats/smooth wheel covers are on my radar. I want to make 'trip strips' but I'll need to look at it a little more closely so I can place them well.
I wanted to tap into the collective knowledge here about side skirt designs. I've noticed quite a few truckers have side skirts on their trailers, the skirt starts close to the inboard tire shoulder of the last axle of the truck and taper out until they're even with the outboard shoulder of the trailer axle. Would a design like this be advantageous to pursue? I was thinking of using some rigid plastic lawn edging and running it from right behind the inner shoulder of the front tires back to the outer shoulder of the back tires. I've got some splash guards I pulled off and could use and a good mounting point for the rear axle if I put them on in front of the wheel. It could also function as a spat with a little reshaping.
Your input is greatly appreciated!

[aerohead]

*If you're not going to cover the wheel openings,then getting the sides even with the wheels might help a tiny bit
http://images.uptilo.com/krtuning/25...A3ABF383BE.jpg
*If you are going to cover the wheel openings,then you need to leave some clearance,especially with the front in order to contain the 'turning' mechanism.