From this image, I'll throw out these recommendations to consider:
1) At the top of the WT, extend the upper panel all the way to where the top of the side panels end, taking full advantage of available ramp deceleration/ pressure recovery.
Now that I know I have decent attached flow I will put on the 22" polycarbonate side extensions and the same for the roof at about 30"
Top & Sides will be flush right at 70" behind bumper with wake width 48"
2) Instead of 'trimming' the lower parts of the side panels 'UP' into a 'scalloped' shape ( like Lawrence Livermore did ), shoot a 10-degree slope, up the from the back of rear wheels, where you first see daylight between the tread and the road ( this will honor the Society of Automotive Engineers' 'Departure' angle of 10-degrees for driveway ramp clearance ), and 'LOWER' the bottom of the side panels, 'ADDING' material, so to coincide with this new imaginary slope. This will give you 'diffuser sides' , for additional pressure recovery at the bottom, not presently available, plus, additional 'maximum' pressure recovery on the sides themselves.
I have not yet gotten to the point I am ready to move the license plate. This kind of limits lowering sides. I am planning a foam floor, 6'L right at the 24" above road height, same as the Van floor. I feel it is the best I can do without moving the license plate.
3) Then, lower the 'floor' down to the bottom of these new sides, to create the lower surface of the added diffuser ( good for approximately 20-counts of drag reduction on a passenger car ).
4) I see that you've added taillights to the sides of the WT, so, other than making the license plate visible, your legal requirements are basically covered.
Not cheap but really happy with the 2nd & 3rd pair of lights. 3rd (rearmost) pair easily repositionable.
5) I can't really see what's going on up top. Those upper corners being airtight, and free of 'kinks', are crucial for optimum flow.
Good enough for right now but not allowing doors to articulate.
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If you can find a 'drone' pilot, with a unit capable of 'chasing' ZEVO at 63-mph, capturing the tuft flow up there, I'll reimburse you for it! ( I have a benefactor who is backing our amateur aerodynamics )
WOW! I will look.WOW!
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PS,
The tuft flow looks really good! I think you're down to just dealing with 'pimples on the elephants behind.' And the tuft 'disturbance' at the bottom sides 'could' be induced from the bow-wake of the chase car. Don't know.