Bill, best to go over to the View/Navion group on Yahoo groups and join there to get the correct info.
We've had 2 Sprinter RV's with the dual rear wheels. It is the pits to check the air on the inner wheel. You do have to remove the stainless wheel covers to check the air. Only issue with that is every time you remove the covers, they get looser & looser with the result that eventually they will come off easily while you drive down the road. You sure don't want that as they are $$$ to replace, even though they are Chinese made.
Best way to solve the dilemma is to install solid brass valve stem replacements on the rears. They are kinda expensive initially, but solve the problem entirely. Borg Tire supply sells them among others. I have a set sold by The Tireman in Northridge, CA. They are wonderful. Takes all of 3-4 minutes to check all 6 tires. Only issue is getting them installed, as they have to be done right the first time, or you have leaks, so you need a good tire place to do them.
One other thing with these is you can't rotate except side to side, as they won't work on the fronts. Fronts don't need extensions anyway.
By the way, this is not a Winnebago issue, it's the way Mercedes supplies them to the RV makers. And don't be surprised if you get these extensions installed that the tire place that you have do them points out to you that the stock stems are not rated for over 60psi pressures. That is correct. Again, the way MB supplies them
Bob & Sharon
Eastern Kansas
2013 Winnebago ERA 70A
Class B Van