What we did that seems to work...been fulltiming for 1 year now:
*We put the sink and shower drains next to each other so they empty directly into the graywater tank. No exposed pipes. Also helps keep the cold & hot water runs short
*We kept the plumbing to one side of the bus.
*We kept the center aisle 36" wide. It feels very roomy (for what it is
*Put in as many windows as possible. Daylight is good.
*A brighter interior helps offset the "enclosed space" feeling.
*We divided the 23' living space into 3 distict areas:
1. The front is the dining area, computer area, cooking area, and my office. Sort of the daytime area.
2. The center is the shower & bathroom
3. The aft area is for relaxing, reading, sleeping. That way we're not crossing over/through the sleeping area to use the potty or get a snack. Very important if your significant other values her sleep
See our website for more info on our conversion.