Frank, you're being difficult. You know the angles and yet don't share them. Why?
The angle on the rear should be anywhere from 15-20 degrees from horizontal, or if you're doing a curved Kammback should follow the "streamlining template", below. Knowing the car is 5,037 mm long you can scale the drawing up for a perfect fit.
Make a cardboard prototype and tuft test it (search the forum for how-to) to see if it's working. Second thought, tuft test the stock car beforehand just to get a feel for what the air is doing!
People usually use some sort of metal structure (Basjoos used aluminum flat iron on the AeroCivic) with coroplast over it. You should be able to get free coroplast at your local political campaign office.
If you can find a spare trunk with that luggage rack on it, you'd probably be a few steps ahead in securing the kammback. A couple small holes are nice but a rack would be great!