A hula hoop makes a great shower curtain rod, and can be hung inside or out.
Mine is also my enclosure for my toilet, which I sit on when showering, since I have a low top van.
Then you need something to catch the water in, I use a storage tote, which can be emptied outside.
For water, you have many options, a weed sprayer, a battery powered shower pump, gravity fed, or siphon pump style like mine. I have a siphon bulb right at my shower head, and then another one in the line on the floor, so that I can squeeze it with either a hand, or by foot. One squeeze = One squirt of water, but if you keep squeezing one or the other, you can get a very nice steady stream. Stop pumping, and it will stop as well. It is a great water miser if you need to be frugal with your water usage. I can stretch one gallon of water out to 3 or 4 showers if I'm careful, and I'm still talking about enjoyable showers.
I can't imagine living without my own toilet & shower...