We only carried a spare tire for our Class A. Those big tires are heavy enough without the extra weight of a rim. Any roadside assist will be able to mount your tire on the rim you already have. We wrapped our spare tire in cellowrap and kept it in the storage area under the bed. That way everything was clean and we did not get a rubber smell.
The one time we had a blowout, it was handy to have the spare tire and Good Sam took care of things.