In our regular body chevy with 24" fiberine top we went with a closet that has all we need to potty and shower inside. My wife actually came up with the idea and we had Van Specialties work it into the interior. Basically it is an area that is ~18" deep (from street side wall) x ~30" wide (to the rear of driver seat) and the height of the van to stock roof rail (~60" ?).
Here is an outside view:
Now again, I must stress... this is basically all my girly-girl MacGirlver's idea. It is so basic and easy to use/maintain. I would have suggested it but, well, it is basically a hunter's dream of a solution to camp-bathroom and I really didn't think she would even take a second thought at the idea...but she came up with it too.
At night we have it in "potty" mode. We use WagBags (commercial and DIY).
and when we want a shower we set up the temporary shower pan and curtain:
For us this is a wonderful solution and has worked well over the last 5 seasons.
Whatever you two decide have fun and enjoy the adventure!
: ) Thom