I use a plastic preasure sprayer. Two people can have a great shower on 1.5 gal of water. Paint it black for a solar shower or just heat some water up on the stove.
I made a cockpit shower stall that hangs from pvc frame from the end of the main boom. Used nylon and made a big velcro "zipper" to get in and out it. Cheap and works great. You will be surprised how well the preasure tank works!