OK, I'll say it. Sounds like a cool project. However, the spoilers on the trunks of cars are not a significant aerodynamic feature when it comes to ecomodding. Even if optimally designed, the spoilers offer only a very small MPG gain. However, they may have a significant impact in the negative light on MPG if done improperly.
Still an interesting project with possible insights for high performance applications with high speed and handling aspects.
It's the overall shape of the car that results in its ultimate Cd, since the trunk spoiler area is such a small part of the overall design, and is in the very turbulent wake area, it's ability to have a large impact isn't that big.
Prepare yourself for only very small variations from one design to the next.