I feel your pain. I travel with 3 kids and up to 7 bikes at times in our Sportsmobile sprinter with penthouse. We all sleep great in it (though we have to put the bikes out at night).
We started with a crew model and penthouse which is comfortable while driving and sleeping. My wife and I sleep up high and the kids all sleep on a platform in the back.
There is little room for much else. You could easily put a porta potty under the rear sleeping platform. We store clothes under the forward part of the sleeping platform and have a kitchen on sliders in the back For showers we use a shower tent with a stove top heated water system or solar shower.
The size of the small Sprinter is great. We can still go through drive-throughs and have no problems with typical height and length restrictions. We had no problems with the Going to the Sun Road in Glacier park for example.
It is a compromise on the bathroom/shower part but the mobility makes up for the inconvenience for us. How and where you stay in the van makes a huge difference.