[jray3]

The following link got me hungry for a true drag reducing spoiler without all the hassle and questionable aesthetic impact of a partial kammback.
]Green Car Congress: Novel Spoiler Design Reduces Fuel Consumption for Minivans, SUVs
5% reduced drag while still reducing lift by 100% sounds pretty good. It didn't specify the mpg improvement. Looks like a good metal beater could make one, or simple enough with rollers if your vehicle has a rare square back.
hand carved foam overlaid with glass? This'un would be a challenge with those knife edges..