My wife & I were campground hosts for 6 weeks in 2012 at Slough Creek Campground in YNP. There are no services at Slough Creek. The park supplied the hosts with solar panels & a 30 gallon water tank with a small 12 volt
pump to transfer water to RV tank. I liked the system so designed my own. (see pics) I bought a 50 gallon flat bottom water tank from a farm supply store (make sure to ask if it is approved for potable water) & a 12v
demand pump, just like the RV uses. I think the whole system cost around $200. I then built a plywood shelf to fit in the bed of our F-150 to set the tank on & mount the pump to. I wired the pump so I can plug it into my trailer 7-pin plug on the pickup for power. I can either fill the freshwater tank on our Airstream, or hook it to the RV city water hook-up & let the demand pump do it's job when water is needed. The tank is out of the way under our topper & we still have storage below it. Another advantage is I always have a replacement water pump along for the RV should I need it. I never travel with water in the tank. When I need water I make a trip with the pickup, fill the tank, then return to camper to fill tank.