[Frank Lee]

You're welcome~

Do you use the truck bed?

Even a tonneau cover provides much of the improvement of a cap. Much easier to build/cheaper to buy as well.

I would imagine, though, that if the angles are right the swoops wouldn't be necessary.

I'd have a preference for a cap's sides to slant in to match that of the cab. I wouldn't care to try to guess the aero penalty a straight up-n-down cap would have vs. a cab-matched one... it's probably not too bad, but if it was me and the interior space requirements allowed it, I'd slant it. Likely the biggest aero penalty would be from the slight frontal area increase... but then again, Ranger greenhouses are pretty vertical along the sides anyway, and the vehicle is almost always in yaw anyway too, so I guess in the real world maybe there is no penalty for vertical sides??? If that's what you wanna build then go for it.

The angle of the "back slope" is the more critical one, and if anything it's better to err on the side of too shallow than too steep. Why? Too shallow an angle will still allow orderly flow down the length of the cap, so the only aero penalty it suffers vs an optimized cap would be a slight increase in the trailing wake area behind the vehicle. However too steep an angle and there could be turbulent flow all along/about the slope of the cap, which would render it pretty much useless. I think what I would do is mock up the cap first, and do a yarn test to see if the flow behaves before committing to the design. Oh, and if the sides stick out some along the back of the truck cab, nice larger radii on the leading edges of the cap should help.