[shovel]

I've worked most of my adult life in industries which put me in direct contact with freight trailers, I have a class A license & drive (commercially) about 20,000 miles per year in a medium duty truck/trailer (48ft trailer/ >24001lb GCW) - not a full 18 wheeler, but close enough to not be entirely naive to the industry.

To me it seems more than plausible to make a standard box trailer whose rear doors are slightly offset, and whose sides are hinged mid-way, to allow the box itself to be narrowed to one door wide at the rear when the box is partially laden or empty. I think this could be done without dramatically adding to the dry weight of the trailer, and without having a significant negative effect on the security of the load or on the driver's docking practices. Visibility (when in aero mode) would be somewhat improved too, which isn't a bad thing.

Would it cost more up front? You betcha. Probably $10k more per trailer and yes, it's one more thing to "go wrong". My guess is it could be done well enough, reliably enough, and repeatably enough to pay for itself in fuel well inside the lifetime of the equipment.