I got the bug, and finished it this afternoon. It actually didn't come out half bad. Passers-by came and asked me what it was, and liked it.
The side supports actually come inward at about 15 degrees, and the kamm is between 12 and 13 degrees. It reduced my rear window view by about 1/3, but it's still enough to see out of. It extends 25" past the roofline.
We'll see how it holds up, and what kind of improvements it has. I already used a quarter tank driving about 80 miles, but it didn't fill all the way to F when I filled up (last tank was 28.6 MPG, surprisingly!). There was a round trip without the vortex generators, so I don't know what effect that had.
Hopefully this will bring me to tank averages at 30 or more!