They sell portable ones that are self contained. I gave ours, from tent camping, to our neighbor that just got a pop up. Good for when you don't want to wander in the night. You might be able to install an outside shower like a lot of units come with. Just a thought. Then there is always the Bumper Dumped!
2012 SunSeeker 3100SS Toad-1962 Futura Average 100 + days camping