I'm not really sure if there's an official standard. Generally, I've seen: * Class B - Essentially built within the confines of a commercial cargo van. * Clas

I'm not really sure if there's an official standard. Generally, I've seen: * Class B - Essentially built within the confines of a commercial cargo van. * Class C - Built on a cab-over or chassis of a medium duty truck/van. * Class A - Built on a heavy-duty bus chassis. ---- EDIT: There's also a class of "Super C" that's becoming more popular. Essentially, a Class C built on heavy duty truck. Great for towing.