Although some small tents that fit over the back of our minivan camper conversion can also serve as privacy, we are actually talking about privacy tents specifically as having a floor area no bigger than about 4 x 4 feet. They are usually a stand alone type tent or enclosure specifically designed to be changing rooms, shower rooms, porta-potty rooms, or all three. They can be “just walls” and open at the top and/or bottom, or they can be fully enclosed.
For our minivan conversion, the ideal thing is to have the rear tent, and then have a privacy enclosure set up WITHIN the main tent for taking showers. The tent itself will serve as privacy for the porta-potty. The one we have is a Bivouac Buddy Shower System, but you have to hang it up. Some tents are not designed for the extra weight, but there is also a stand for the Bivouac Buddy that allows it to hang anywhere, even inside another tent. The drain pan at the bottom has a hose fitting on it, so you can drain the water away from your tent area. However, the unit is only 34 inches in diameter, so it doesn’t make a good porta-potty closet. When packed up in its carry bag, the unit is 34 inches in diameter and about 2-inches thick. The stand can be taken apart and stores in very little space.
However, we usually pack it in the very bottom of the space under the couch/bed, because we normally use our membership park system and the nice clean restrooms that they provide. Our shower is more like an “emergency last resort” type of thing when we don’t have anything else available, and that’s not very often. But if you like traveling in remote areas and camp out in the wilds, the Bivouac Buddy System, inside another tent or free standing works very well. Combined with the “on demand” hot water system that we recommend and it’s almost as good as home!
There are free standing units that are square and have a little more room, so they could be used for a porta-potty AND an shower, but not all of them are designed for showers. Some are too big to be practical to use inside of another tent, but would work well outside, as a separate tent. Make sure whatever you buy will work for your intended use.