First storing a couple hundred gallons of water, in the sun is not the best idea. You can very easily get thing "growing" in that tank ! Drinking and bathing water need some SERIOUS treatment ! Possibly chlorine or at least ozone and/or ultraviolet.
If you plan on spending a lot of time there, a small structure housing your treatment equipment and typical home jet pump and pressure tank are your best option. I am sure you can find an "off grid" 12V pump.
If you own the property, I would make the structure big enough to house some batteries and maybe even mount some solar panels on the roof.
Solar panels on the roof of your RV and more batteries would allow you to run a residential refrigerator without a generator. Again, I you own the property, a carport like structure to keep the sun off of the roof of your RV will make a HUGE difference !