IMO it is the radiant heat from your exhaust system that is causing your tire to always run a bit hotter.
Remember that the "aging rate" of tires doubles with each increase of 18°. This means you are potentially cutting the life in half.
I suggest you take a look underneath your coach. You do not need to wrap your exhaust. This can cause problems and may shorten the life of your exhaust system. A simple metal shield can shield the tires from the IR heat.
Here is what GM installed on my C4500 for my Class-C. Simple sheet metal with a bottom lip to provide some stiffness and to prevent cuts I guess. Just some galvanized 16 to 20 Ga steel can do the job. I bet if you check with a Home heating shop that does ductwork they can cut and bend a piece for not much $. My shields were welded (1" every foot or so) and show no signs of failing after 17,000 miles. Could also drill and use some heavy metal screws too.