I have industrial experience with RO systems and I doubt one would be appropriate for an RV. For one thing they generate a waste stream of the concentrated wastes from the material removed from the influent water. Also I would be surprised if they weren't major energy hogs. You need to determine the amperage draw for these units.
The household units placed under the sink to provide low volume supplies of drinking water are toys and I doubt will be filling your 50 gallon water tank. RO membranes have a definite lifespan measured in gallons passed thru them and on the quality of that water.
These days your enemy with untreated water is giardia spores. Along with other things like cryptsporidium. Usually chlorination or some other disinfectant is needed and even professionals running municipal water systems can fail to remove all of these microbes. And that's with the regulators breathing down their necks.
There is a low energy and fairly low tech method, sand filters when properly constructed and operated. Not very portable and the effluent still needs chlorine or ozone (high energy requirements). And knowledgeable monitoring.
WikiPeople credit doctors for curbing infectious diseases. But a big part of that reduction was derived from engineers constructing safe water sources for people to use.
My suggestion: buy some big water drums, 30 or 55 gallon plastic drums and get you water from a safe source.