[mpg_numbers_guy]

Looks good!

1. Check your state laws. Some require just a passenger mirror, others only require a single rearward facing mirror. As long as you're following what the law says, they can't ticket you. Rearward visibility can't be obstructed though, so you can't pull a trailer or tint your rear windows. I haven't gotten pulled over once yet despite probably dozens of police officers seeing my car.

2. On my Civic I used coroplast, attached with zip ties, painted flat black.
48"x96" sheet of Coroplast: $23. 4x15" diameter discs = $3.53 (cost by area; extra plastic was used for other projects)
Can of rattle black paint: $1.99
Pack of 100 zip ties $8.99. 4x4 per wheel = 16 zip ties = $1.44
Total cost: $6.96, and I used the paint for many things after, so let's call it $6.

3) Driving style is number one, fuel economy instrumentation is number two, and tire pressure is number three. I drive a 2006 Honda Insight but this is true for pretty much any vehicle.

4) The Insight attracts some attention due to it being a unique and small car. The Civic I owned attracted more attention because it had many more visible modifications.

What do you like best about your Volt? Cowmeat on here has owned a couple Volts, and it seems like the EV range can be extended quite far beyond stock through good hypermiling.

How is the underbody on the Volt? IIRC from what others have said, the stock underbody is already quite smooth, so you may not see much of a benefit from an air dam, which is usually a quick-fix for cars with poor underbody aero. You may see more gains from finishing the underbody than from adding an air dam.