Nice diagram.
The catch with skoolie floorplans usually turns out to be gray/blackwater tank locations, and getting liquid to them via gravity. The locations of existing fuel tanks, chassis rails, and wheels/axles/wheel humps are obviously key. If you have an underbelly plan, you should be good. Also make sure your vents (fresh & waste tanks, and any propane appliances) are accounted for.
HTH,
Sean