Consider looking around for some Van Clubs around your part of the country. They will likely know carpenters who have built out some Vans like those back in the late 60's and through the 70's. They have meetups each summer too.
Then it would just be a matter of how "built" you would want it to be.
My own angle on this is shown in my first website below, where the shower, toilet, and laundry with the water storage, water heater, generator etc are contained in a small Cargo Trailer such that in a space of about 23 ft
you have the utilities half which can be detached and parked while you can go touring in the Van for a couple of days. You can cook and sleep in the Van while you go sight seeing and return to the Trailer to freshen up, clean clothes etc before hitching up and traveling on. You have the best of both worlds of a Big Class C and the flexibility of a Day Tripper or Weekender Van to go sight seeing in, and do some light camping.
The trailer could be stored in or at a paid parking facility or in a secured campground while you go sight seeing
and be ready for you hitch up to when you come back. Your Van rig could be built stealthy and the trailer wouldn't give it away when you have left it behind.
There are plenty of clean public restrooms when you are traveling in just the Van. By using a 2 gallon garden sprayer painted black, (that you would carry in the Van) you could find a private place to take a quick shower, while away from the Cargo Trailer. It's just a thought.
