Looking for some design guidance on hitch rack/ boat tail for Model S
 

I’m mainly not sure how the Template should be overlaid on my car.
Planning on truncated end with about 8” height remaining. Total length off rear bumper needs to be just under 4 ft to haul needed cargo. It can’t taper more than 6” per side (looking from above left and right) also to clear cargo.

Car is 2012 Model S P85, cargo is a stack of display panels and EZ up tent.

I always figured one of those triangular trailer tool boxes would be a good starting point.

tail
 

The Daimler-Benz,Mercedes-Benz,1977 C-111,II record car was Cd 0.237,close to the Model S.
For 1978,they added 600mm of boat tail,and the drag dropped to Cd 0.195,for a new world record speed.
They had analyzed the car with up to 1,500mm of tail,which got them to Cd 0.178.
No tellin' how the S will respond to a boat tail,but we never know 'til we try.
What a great project!

boat tail
 

We just re-did our You-Tube video for boat-tailed Tesla Model-3.
At You-Tube,you'd do a search for John Gilkison.When you get there,it's 3rd video from the top.

Depends on how you search. If you go to his home page it listed first.

https://www.youtube.com/watch?v=azQg1-xyJAo

It shouldn't. Look at it from the end, it's a half-circle. You are starting with an existing cross-sectional profile. Six inches of taper in 4 feet is you limit. If the top tapers faster than the sides air will migrate upward and potentially induce vortexes.

A smooth transition onto a compound curve will do the most good. How does the cargo load, from the rear or side?

I've try to get some material on boat tail vs box cavity vs retractable base plate.