Some argue that There is NO B+. If the house isn't included in the van's steel body, the house built on a cutaway chassis makes it a C. Cabover or not. There's merit to that position, but...
... most B+ are a little smaller than a C with the cabover. The coach MAY (not always) be Lower, Narrower, and offer less Storage. Since both are a big box, it can be hard to tell unless they're side by side. Check specs and take measurements.
Example new Cambria 30J. Over 32-ft long, width is 95-in while most C's are 101-in. With it's 220-in wheelbase that 30J should have enough front axle loading to track well on the road ...