What happened to the old, square, collapsable, plastic water carriers with a handle on the top, and a spigot ? The optional extras were a long hose that attached to the spigot, with a shower head on it.
You put the water carrier on the top of your trailer in the sun,
and a couple of hours later you donned your swim suit, and took a shower. Another extra was a portable shower curtain rail that attached to your trailer.
I think they were called 'solar showers'. Now, that's
boondocking !! No utilities needed.