I'm not aware of any hybrid motorhomes actually being made. That's not to say they don't exist; I had not heard of the Fleetwood/Winnebago/Freightliner work, so I'm far from fully informed on the matter. These days I would imagine the most likely source for one would seem to be a conversion from a hybrid city bus.
In general, the fuel economy improvements of a hybrid drivetrain are mainly under the sorts of conditions where motorhomes are less likely to be used: start and stop city driving rather than extended highway cruising. In my mind, the main advantages a hybrid motorhome could offer have more to do with the possibility of integration with the house systems, particularly the house electrical system. If the hybrid battery pack were also the house battery, there would be a lot more power available than typical, making an all electric coach more practical for boondocking etc. Presumably the main engine could also serve double duty as the generator, recharging the battery when needed, and saving the weight and maintenance needs of a separate generator. My suspicion unfortunately is that many RV makers would be fairly slow to adopt that sort of integration if they did offer a hybrid motorhome.
It would also be nice to be able to quietly trundle in and out of a campground at night (without having to start the engine).
