[freebeard]

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?