Some years ago,(1980) I installed a device on my 1980 Econoline called a "Compu-cruize". It measured fuel to the 100th of a gallon, running MPG, calibrated speedo, and a bunch of other FUNctions.
I was surprized to find that the most efficient draft point was at a reasonably safe distance behind a full sized semi-truck at 55MPH which was the interstate speed limit at the time.
Too close was actually worse than no draft, too far simply eliminated the effect, but just right would add a surprizing increase to the running MPG. The key ,of course, is air management, at the point of most efficiency there is a low pressure area behind the lead vehicle.
With similar vehicles like racecars the sweet spot is intense tailgating, but with the huge difference in size and shape the Semi leading the Econoline allowed for a safer distance.
There are several reasons why "drafting" is a bad practice today however. even if you leave out "following too close".
1] Today's higher speed limit changes everything.
2] There is no longer any such thing as a slower moving truck![lol] if it is "slower moving" it's probably broken.
3] Visibility is restricted when following a truck and this could be dangerous for traffic and also for seeing traffic signs [you'll miss your exit]
4] While tailgating is ill-advised for collision reasons, it is even more dangerous to follow a truck because of crap coming off of it, like tire tread, broken brake drum parts, belly spares, chain binders, or cargo. not to mention sheets of ice in the winter, or road debris kicked up by those big tires
5] Benefiting at all from "drafting" requires attention which is better left to traffic or even scenery and isn't worth the effort or the risk.
6] With a trailer, which is pretty much "drafting" your TV anyway, the issue becomes complicated enough that it would likely result in a loss of efficiency.
7] Your rig will get filthy and chipped up by following trucks, keep an open road in front of you whenever possible.
While even geese and bicycle racers benefit from drafting there are few occasions where you could experience any real benefit from drafting while towing.
Best efficiecy and lowest fatigue comes from slowing down, relaxing, and keeping your distance from all traffic.
And , as the song "motorcycle mama" says..... "and if the squares want by, then we'll let them pass"
then you can feel like "the queen[or king] of the highway", you'll see the world from your RV.
BTW; whose driving do you trust anyway, the stranger in the truck??
While there are many great truckers with good equipment out there, there are plenty on drugs, alcohol, or tired, with broken trucks and bad attitudes.