RIVA does not reconize a B+ as a Type of RV. It is a made up manufactures term for a small Class C.
A Class B started out as a van, after that it doesn't matter what is done to it.
A "Type" of RV is based on what the original chassis is, not what the body was altered to look like.
This is RIVA's definition of a Type/ Class B.
"Commonly called van campers, Type B Motorhomes are built using automotive manufactured van or panel-truck shells"
This is the definition for a Class C.
"Type C Motorhomes are built on an automotive van frame with a wider body section attached to the original cab section." Also called a cut-away chassis.
Some manufactures call their 35' 3 slide Type/Class C a B+. So you see size is irrelevant to these manufactures, they consider anything without a cab over sleeper a B+.
Now I know some of you don't want to accept RIVA's (who sets the standards for the RV industry) definitions, and that's fine as it always seems to get people talking which is what a forum is for.
Ref.
RIVA's consumer site