Hi gbopp,
I emailed that source--I've not heard back from them yet. I surely would buy one, if that were an option.
I do have air tabs and they do help--mostly they cut down on the wind noise inside the RV. I do get between 10 and 11 mpg (US) if I drive 49 mph.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.