According to txdps:
2. Class B driver license permits a person to drive the following vehicles except a motocycle or moped:
a. a single unit vehicle with a gross vehicle weight rating of 26,001 pounds or more, and any such vehicle towing either a vehicle with a gross vehicle weight rating that does not exceed 10,000 pounds, or a farm trailer with a gross vehicle weight rating that does not exceed 20,000 pounds.
b. a bus with a seating capacity of 24 passengers or more, including the driver and
c.. a vehicle included in Class C
No gray area here. And I found this out in the course of conversation with a Texas cop who was stopped in the KOA in Colorado Springs who happened to have the RV next to us. I checked with the state and it was confirmed. It's in the book from which the written test is derived. But it is true that many do not know or have the class B license, including me for 5 years. Unless you ask, you won't know if you are transferring in from out of state, even when you are registering your coach purchased in another state. It appears to be ticketable offense if one is driving such a coach without at least a class B, in Texas.