This may help a few of you. It's a free download of the Tumbleweed Tiny Houses catalog. Some of the towable houses may have floor plans that you can use with a little modification or help you to create your own. http://www.tumbleweedhouses.com/pages/freebies
Yes, I know it's not buses but the tiny bathrooms and kitchens may help some with imaging something that will suit their own situation.