My brother has a pop up pickup camper. It came without a shower, but there was room for one. He took a new 1 or 2 gallon garden sprayer, replaced the spray head with a RV shower head (on and off valve on the head).
He fills it with warm water, pumps it up and showers in the shower space he improved.
Wet down, soap and rinse. Easy. He tells me they get two showers out of a tank of water.
The same system, set up in a privy shelter, would be light and compact. I intend to follow my brothers example for my tear!!