I played with one of those small round units that had several blade around it much like one of those roof mounted heat turbines on houses. This would spin up and turn a shaft going down inside the RV unit. Then a alternator like device would charge your batteries like the automotive type chargers do... It worked to some intent but only reall would work going down the road at 60mph haha... This was when I was living in Texas that alwys had at least a 5MPH wind blowing. If one lived on the coast or near the mountains it might work just sitting there...
Solar Panels are the best way to go for sure...
Roy Ken