About those renderings. I would point to
Compact camper alternative:.... If I could detach the hatch in that model, I'd have it open like a Type II ambulance (hinged on the bottom) and fill the gap with ribs and canvas like an old Model T Touring.
[The reason the Thanks button wasn't working was you can only press it once. Who knew?]
Maybe there's no published examples in the automotive world, but it turns out Dumbo Octopuses do it.
Plus which:
Edit: Here're these ones, too. Half-circular cross section instead of a squircle.
Coanda nozzle vs high-tailed stinger:
