i fillup during my arrival at the campground if the line is not too long .. It there are two or more trailers .. i use a water-thief (see google), collect my water from a spiggot in the campground into some 5 gallon containers, then off load them via gravity from the back of my pickup to the water tank
Works perfectly ... and a great idea for those "over 4 night stays" where a water fillup is required .
2008 Nissan Frontier 4x4
2011 Rockwood A122