[aerohead]

Historically,with the exception to wing-form bodies,the K-form aft-body continues to demonstrate the lowest drag.
*It has no separation
*It generates zero lift
*It's modular.Once you've established the essential Kamm architecture,you can simply add additional elongation for additional savings.
*You will have a blind spot on the passenger side unless you provide for a fenestration there.
*And the new backlight,if part of the roof,will be so steep as to block outward vision.A vertical backlight,with louvered cover has been a repeated solution.
*Rear camera systems are a big plus.