I added the DuallyValve valve stems to the four rear tires when I had the tires replaced a few weeks ago. The are pricey - $118 - and the tires have to be dismounted so they can be installed, but for the peace of mind and very easy air check and inflation they are worth it to me.
I got mine from Borg Tire Service but as Linda says the Tireman sells them also although he doesn't seem to have them for the Workhorse chassis. If he does I couldn't find them.
I had the braided wire covered extensions that came with my coach for 6 years and had no problem with them, but a leak in a similar extention on my last motor home caused a blowout. I was nervous about the braided ones on this coach for all six years.
Clay WA5NMR - Ex Snowbird - 1 year, Ex Full timer for 11 years - 2004 Winnebago Sightseer 35N Workhorse chassis. Honda Accord toad.