Bill.....Those are for coaches that are using one piece stems (no extensions). They won't do anything for your extensions. Your extensions should be bolted to the center hub.
I disliked the look of the extensions on my 22.5 Accurides, plus they made it hard to polish the rims. My extensions never leaked, but I replaced them with a long valve stem. I see people recommending the "Dually Stem" which I think are over a $100.00 dollars a pair. You have to be crazy to pay that. I went to a local tire store who had 8" valves that fit my rims for $11.00. I later found them online for $8.00.
I didn't like the looks of the plugs you posted either, so here is what I did to support my long stems. I made a support for the stem out of a piece of thin aluminum. I mounted it over the studs between the inner and out duals. This is the template:
This is what it looks like installed:
On the outer wheel, I just turned the original metal stem around, but wish now that it would have been replaced with just a short straight stem:
Don & Mary
2019 Newmar Dutch Star 4018 - All Electric
2019 Ford Raptor Crew Cab