We debated on how to add a shower to our plumbing system, but decided to go another way.
We tried the gravity feed bag showers, but not enough pressure, and you have to find something high to hang it from.
So, we got the Helio pressurized shower and have loved it.
https://www.rei.com/product/882468/n...ressure-shower
We fill the bag with hot water from our sink and pump it up. We use about 2 gallons water and that is plenty of hot water with the pressure from the nozzle. We could also fill it up from other sources if available.
For privacy we use a shower tent. This one has been awesome, but there are many options available.
A big advantage over an attached external shower is we can pick our spot where we set up the shower, so we don’t have a muddy spot by the van door.