One feature I'm working on and will have live soon is a water pump..
Ok story: the OEM water pump started having issues so I put in a new onem, Old one still works but it needs some work (leaks in operation) so.....
I'll rig it to pump water from a container either in my car or on the ground,, Get a bladder (likely 40 gallons, but they make a 90) and pump away when I need to on boondock sites.
That said... I routinely haul 80 gallons of water when traveling, or less.. Depends on how long between water faucets.
I'm not so sure I'd want to fill at a Gas station but here is a thought.
Leave one day early, Spend one night, just one, in a campground NEAR your target.. Pay the 20-40 bucks, tank up, empty waste tanks (if needed) relax and finish the trip in the AM.
Personally... I'd haul water
ADVANTAGE to hauling your own water..... There is a condition often called Montezuma's Revenge.... The cause is often the difference in water between what you are used to and where you park.... I've had it.. Back in my part time days.
I use filters (Activatec charcoal plus PUR) and that minimizes it, but that's a STRONG argument for hauling your own water.