Based on this forum I purchased an aftermarket TPMS system from Tymate:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
On our last trip on of our dually tires on the back of our Class C got a fast leak in it while driving. Amazingly, we had just entered a populated area with tire stores. The valve stem decided to die. Without it, we would have not known until we stopped. Saved us damage and was a safety issue. The fix was free (although I did tip them), if we drove on it I am confident it would have been more than the cost of the TPMS unit.