I didn't know exactly what model you had, but it looks like the epa combined is in the high teens or up to 20 mpg, and since many of us regularly exceed the EPA estimate by 20-50%, I think we some effort (and just driving habit changes), you could pop up into the mid 20s. Of course, I'm just guestimating, but I'd say it's certainly possible.
Wheel covers look like this:
http://www.autowonderland.ca/index.a...ROD&ProdID=524
They work to cut down drag from the wheels...might not be too necessary for the back if you have skirts, but I'd do it anyway...I'm not an expert on wheel well turbulence by any means. You can also DIY them out of pizza plates or something such if you're up to it.