What did you think of 2000neon's solution:
The sides are important to the aerodynamic performance. You need to get the right taper and tumblehome. A lot of rear visibility will go away, three cameras would be better than one.
Are you still planning on making it a liftback? Chevy Nova did that in 1974 as an option to their standard notchback.
You could research what they did to stiffen the body.