Well I had one on my car for a while. Here is what a Found:
1: start the slope to match the areo template.
2: slope the sides in at about the same angle.
3: round off the transition from sides to top.
4: start planning for a boat tail. Once you try the kammback and find a minimal improvement you will want to add a tail to the car.
5: how are you going to attach the Kammback? those mount points might be good for a tail (add a hitch for the lower point).
__________________
|