Search for posts made by @AltoGrayhound and I believe you will find that he experimented with implementing what you are discussing.I’ll have to browse through Model X Travel Trailer Consumption Analysis thread linked above because I’ve always felt the “missing link” to solve for improving range was the pocket between the X and trailer. Wouldn’t the air flow in there cost significant range?
Unfortunately, I have to believe that if that were true, someone would have invented a plastic pop-up cover to connect the towing vehicle and trailer to minimize that flow. Kind of like the super advanced schematic I added to @AltoGrayhound pic below.
Your interest in trailer aerodynamics and concern about the “gap” between tow vehicle and trailer is very reasonable. I suggest you post in the Model X Travel Trailer Consumption Analysis thread, as this thread is for discussing currently available trailers that are best suited for towing with an X.