Just my 'sperience, Hank:
I ordered solid (chrome plated brass, I believe) "Dually" valve stems from here:
https://www.shinyrv.com/product-category/dually-valve-stems/ They have a "CONTACT" button on their site.
I tried to go to the main supplier for Dually Stems, but they wanted to know what angle I needed. I didn't have a clue, so I contacted the folks at "Always Shiny" and they knew exactly what I needed. IIRC the price back then was $115 with free shipping. I had them installed on the duals at Les Schwab ..... for about $85 (they said an easy job cuz all they have to do is "break the bead" to install....no tire dismount needed.) Know that it is nigh impossible to spin balance the inside dual with the 7-inch long valve stem so I installed "Centramatics" ....... I now doubt that was needed as some folks do not balance the rears at all; probably could just spin balance the outer dually and call it a done deal.
The hardware from Always Shiny included a rubber "stabilizer" that goes in one of the "hand holes" on the Alcoa rim to stabilize the long inside stem. I wasn't thrilled with the fit on those stabilizers, but they have never moved.....so they work.
I use a TST system with the cap sensors. Never had a problem since installing this setup about 3 years ago. One nice feature: I can check the pressure or air up any tire without even getting down on one knee...... so I am well satisfied. I personally like the cap sensors better than the flow through type (I've used both) however it is a bear to service the cap sensors with new batteries, and O-rings (the flow throughs are easier) ..... but I go ahead and do it each winter for the upcoming travel season.
I didn't need to do anything to the steer tires to use the TST cap sensors. A little tight, but not real difficult to install or remove the sensors. I did modify my sensors by removing the "theft prevention' feature. Simplifies things, IMHO.
Hopes this helps. As always, YMMV.
Stay safe.
Ed Sievers, Denver, CO
07 WGO Outlook 31-C; '16 Kia Soul with 6spd DIY Tranny
"Be the person you needed when you were younger"