FWIW, I've drafted on a bicycle behind a van, and as long as I was within about 3-4 feet of the van I was basically traveling in still air, but any further back than that, and lots of air resistance. That was up to 55 mph. That's what makes me pooh-pooh those deflectors that mount on most trucks: they're just too far away from the trailer to do much of anything, and they're at such a steep angle, they just act as another air stopper. They may throw the bugs over the top, but the wind is just going to curl back around and continue on into the front of the trailer.
IMO Maurice's air deflector looks like it would work because it ends close to the front of the trailer, and is a more gradual slope than most of those add-on wind deflectors. JMO anyway.
