The ones you need are from Borg AKA Your Tire Supply.
Dually KitThey will look like this. They are cheaper than the ones linked above and come from the company that was one of the original makers of longer valve stems for Class C Duallys. I have a set from another vendor that was the original maker of them and have been on my Class C for over 10 years with no leaks or problems. You can Check the pressure on all tires in a matter of minutes.
Valve stemsDO NOT put the braided extenders on, they will leak and if they come loose from their mount on the wheel they will cause a catastrophic air loss.