I was thinking about prior to your road trip and tuft testing, before you commit to the final shape. Only trying to be helpful, not contrary.
It looks pretty good. I'd radius the horizontal edges because otherwise the smooth wake your working for will be disrupted in the last foot. It might anyway, that notch is big enough for recirculation.
The forward facing fins are called Vortex traps on semi-trailers (lower right).
You might put clear plastic vortex traps in the taillight cutout, now that I think about it. Are you going to have turn signal repeaters?
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Good sense, innocence, cripplin' mankind
Dead kings, many things I can't define
Occasions, persuasions clutter your mind
Incense and peppermints, the color of time
Who cares what games we choose?
Little to win, but nothin' to lose
"Incense And Peppermints"
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