I also miss the outdoor shower that I used to have in my truck camper.
Here's a lot cheaper & simpler option:
Of course it's only cold water, and it only works if the campground has water hookups, but it might work for you.
Just a thought -- if you do install an outdoor shower, be sure to add an outdoor water pump switch. Every time I had sandy feet and wanted to use mine, the water pump somehow sensed this and magically got turned off, and the switch was inside by the sink, well out of reach to someone standing in the doorway, trying not to get sand in the camper.