z..geo - Good question. First thing to consider is the weight ratings. According to the RVision brochures, the Chevy chassis all have a Gross Vehicle Weight Rating (GVWR) of 12,300 lbs and the Ford chassis have a GVWR of 10,700 lbs. This is true for all models. Then there is a front axle rating (GAWR) and a rear axle rating. The tow hitch is rated at 5,000 lbs with a tongue weight of 500 lbs. These are all maximum ratings and none should be exceeded - however, most Class C's exceed these maximums. Not a good thing, just fact. When a unit is produced it has an unloaded weight (will be different by the different models) and then the customer adds options (i.e. awnings, air conditioners, heaters, ladders, generators, etc.) which will affect the shipped weight. Then the owner adds personal belongings, supplies, people, gasoline, propane and water. This will now give you the curb weight. The additions all vary based on the wishes of the owner. The only way to really answer your question is to get the curb weight of the unit you are looking at (good guess on what you will add) and then subtract from the maximums to see how much and where you can carry the weight of a motorcycle.
I too prefer to have a motorcyle as my TOAD. I have chosen to haul on a light weight trailer. My road bike weighs around 600 lbs and I just felt it would be too much for the hitch even if re-inforced. The trailer is not even noticed when being TOWED.
As to being in the correct topic, It seems like anything about a B+ should fit this topic as that is the title. I am guilty of answering and asking a lot of different things in this general topic.