Stumbled on two interesting tidbits relative to leading edges on square boxes, particularly RVs and box trucks.
First is the first attached image. Just wrapped up a 2 week RV trip. Saw a few late model Jayco Class C motorhomes on our trip. Didn't take picture myself (should have) but googled a random image and attached it. Google says a Jayco Redhawk or Greyhawk has the feature. It's the leading edge/face treatment of the box near the cab doors. The rounded bubble is only part of the face piece. There's a"normal" square edge beneath it. I can't say that it is an aerodynamic device, but it obvious to me it would help. Maybe it was done to improve the wind noise or something.
Second is a document I found searching for some information on frontal area tow ratings from the manufacturers (yes, some do spec frontal area in addition to weight for tow ratings). It's Ford service bulletin about the frontal area and weight ratings for the 2017 Ford cutaway van.
https://www.fleet.ford.com/truckbbas...ml/Q-246R5.pdf
Note that it specs a 2.4" leading edge radius for box type trucks over a certain frontal area. We know 4% of the width is a minimum, that'd be slightly more than 2.4", but very interesting to see something like this directly from a manufacturer. I suspect there's no engineering behind the number (too bad). I'd guess 2.4" is probably what someone like U-Haul uses on their boxes, and Ford grabbed that as a working minimum. U-Haul does claim aerodynamic leading edges on the advertising of some of their trucks, so the story seems to fit.
There's also some ridiculous 1700mm spec for the stripped chassis. But this too appears to be a number grabbed from a manufacturer. The only RV built on the stripped chassis right now is the Thor Axis/Vegas. It's been around a couple years now. Note its shape below...
So maybe the Jayco devices help them meet the new Ford restrictions? I've only seen it on a Jayco, so far.