I guess folks forget physics real quick.....MPG is a factor of distance traveled and if you reduce wander and steering corrections, you reduce distance traveled, so in theory, MPG has to increase.
The trucks I saw on I-80 and I-84 were trucks from large fleet and are just like trailer skirts 3 short years ago, which were slow to catch on, but today 90% of the trailers out here are running side skirts. I have no idea what the companies east of the big ditch are doing, but west of the ditch, they are starting to understand laws of physics and the price of fuel.
There will always be the naysayers, especially those that refuse to understand what a vortex generator does and why they would work on an RVer, which is fine. But to blatantly state it is Voodoo reasoning, is absurd.