Yes, I know am l8 2 the party, but I don't get to areas w/signal much.
This is how I've showered for yrs. YMMV
I have those pole + wire shelving racks outboard (on each side of vehicle, 36 in wide x 14 in deep) where I store my stuff. They're braced on the top shelf, next to ea pole w/ (2) 2x4, which goes across the aisle.
So, my shower consists of a contractor bag + a sprayer. When I open up a new bag I place 4 "tabs" of duct tape along the top edge of bag, to give the binders a surface to grab. I use a piece of string (5 ft length currently) & knot a binder clip on ea end (x2). Throw the strings across the 2x4s, attach the bag w/binder clips after I've stepped into bag (after setting up the sprayer). I use another bag (opened) to dbl bag, JIC.
I bought a 50 ct box in Apr '18 & still have about 40 left. Since there's very little friction & no objects to puncture the bag, they last quite a while. Once the bag does start to wear, I use it for blackout curtains, poncho etc.
When it fairly warm/sunny, I set the bag (in my chair or on picnic table); I put a couple gal of water in the bag & set it out in the sun to warm. Pour water into sprayer once it's desired temp.
Once bag is drained well, fold & roll it up til next use. Doesn't require much space to store the whole lot of bags.
It's just a thought. Enjoy.