Doesn't sound like ANY gain to me. We had a 1997 Discovery diesel pusher with a Banks kit installed on it in California. I average 12mph highway with it. We even drove from El Paso, TX to Las Vegas, NV non-stop. I think it was 900 miles with fuel to spare. On that trip, we got over 13mpg!

It's unfortunate that their hybrid spokesperson doesn't understand hybrids.
Does it operate like a Prius or does it operate like they described it here? That could be important depending on where you vacation.

But was it the Class A (the largest) RV? They don't give the length and weight of the test vehicle, unfortunately.

I have a 1994 Airstream Classic 360TD Class A motorhome which has a Cummins 230 on a Sparton chassis. It's 36', weighs 22,000 lbs and is the last of the aluminum sided Airstream motorhomes (they still make aluminum sided trailers). I bought it in September 2002 with 44,000 miles and was initially averaging 9 mpg. I added a Banks Power Pack system in October 2002 which reportedly provided an additional 94-hp and +241 lb-ft at the rear wheels with a 12% gain in mpg. I never dyno'd the rear wheels but have been averaging 11.5 mpg since the addition as I now have over 165,000 miles. For the past 20,000 miles or so I have been primarily using B-20 biodiesel though this depends on availability as I travel.

I lived in this motorhome from September 2002 through October 2007. The vast majority of the time I was boondocking (drycamping) on private property as I mounted 4 120-W solar panels on the roof and rigged a portable AIR-X marine wind generator to provide for my electricity needs. I use propane for refridgeration, hot water and heat including 2 catalytic heaters that use no electricity. I found this system successful even through the New England winters.

I certainly welcome finding new ways to improve the efficiencies and lower carbon foot prints for future RVs as the independence is truly liberating. I still have the motorhome but now am only using it for several longer trips per year when the family is travelling along instead of the regular travel that I had been using it for with business and pleasure.

It was a 37 foot Class A with the big slide. 325hp 5.9L Cummins diesel with 6 speed Allison. It was all OLD technology.