HOW IS YOUR CRYSTAL BALL?

Wind turbine on the roof ...

The physics of this situation is that a wind turbine on the roof will take more energy than it will produce, just like an alternator on the axle.

When DH and I were in the electric vehicle business, I lost track of the times someone said, "I don't understand why you haven't thought of putting a windmill on the roof" (assuming we hadn't thought of that idea that wouldn't work) or "... an alternator on the rear axle," which has the same problem. It was always the rear axle. We could never figure out why they thought an alternator on the rear axle would work better than on the front axle. :h

Maybe the poster of the wind turbine comment was joking, but you would be amazed at how many people seriously suggest this idea and never can understand why it is a joke.

I won't get started on solar. Yes, it has some good uses, like keeping the battery charged.

LNG is being seen as the future in a lot of larger horsepower applications, such as ships, ferries, tugs, and supply boats, as well as power plant back-up power generation.....but I just don't see it in the RV industry, unless they can come up with a more convenient method of filling the tanks. With gas/diesel, you have multiple choices in almost every small town in America.
I just don't see that happening with LP.

I do believe that wind and solar have future applications, if the prices come down, but as mentioned, it's not going to run your RV. Maybe a few panels or a small windmill to operate the television or inverter... but not much else.
I see it at your stick-built, but not the RV.

Mine is pretty cloudy but since CNG has been around for many years and has never become a serious fuel source, I'd guess it likely will not in the future. MIGHT be a more serious fuel source for boats since CNG is lighter than air which prevents it from accumulating in the bilges and becoming an explosion hazard as LPG does.

Wind turbine on the roof is going to present a problem with tunnels and overpasses, plus you will have to park at the top of a hill to build up enough speed to get the wind turbine cranked up. :B

CNG requires very expensive (initial cost and ongoing maintenance) compressors at service stations. These costs are not excessive for city locations but would be an a heavy burden for low density highway locations. IMO.

Nope. Solar and wind will be future.