Can't speak for the Class A's, but on the Class C Duals, we started using a product called "Air-Flexx". The problem with most extenders is that they are "pressurized", when you screw them on they open the tire nozzle and move the seal point to the end of the extension. If they flop around rubbing on the rim and break...then the tire goes flat. If they get loose, the tire goes flat.
The Air-Flexx is rigid so it needs no clamp and it is not pressurized...there is a metal shaft that goes from the end to the tire nozzle. When you push the metal shaft, it then opens the nozzle on the tire stem. You can cut it in half and the tire will not leak. Our blown tires due to low pressure and warranty claims on leaking extenders is now non-existent. They're made in Germany, but when we started using them they set up a US distributor.