Keep in mind the metal valve stems can be rotated allowing the open end to face in any direction. The ones on the inner duals of our 2013 Adventurer were facing outward, but not where I could reach them with a tire gauge. I had to slightly loosen the nut and rotate them so they faced the center of the hole in the outer wheel.
Even then I couldn't get a tire gauge or inflator on them properly because of the smaller hole in the outer aluminum wheel. Rather than add valve stem extensions or change out the stems themselves I modified my Milton 506 inflator gauge to reach through the outer wheel and fit the inner valve stem.
Milton Window Inflator Gage, Dual Head, Model# S-506 | Air Chucks Gauges| Northern Tool + Equipment
Milton also makes a 516 inflator gauge. In our case I needed the forward facing angled foot of the 506 to make contact with the inner valve stem.
Milton Window Inflator Air Gauge — Dual-Head Straight Chuck, 1/4in. Inlet, Model# S-516 | Air Chucks Gauges| Northern Tool + Equipment
I replaced the 6" brass tube between the foot and flexible hose with a 12" piece of 5/16" brake line and a couple adaptors to fit the 1/8" pipe threads. Then I made a slight S bend in the tube to allow it to fit through the wheel and seal against the inner wheel valve stem.
I could have added valve stem extensions or gone the dually route, but it only took about 1/2 an hour to make the modification to the inflator. I don't have to deal with extensions or find a way to support them or the dually stems. Also I have a compressor at home and one in the motorhome so I keep the modified inflator with the motorhome.
As a side note your rear inner duals should be identical to the fronts if you have steel wheels. If you have aluminum outer duals and front wheels the valve stems on the inner duals should be facing the same direction as the ones on your front tires. I'll bet someone at the dealership rotated the rear inner dual valve stems to a position where they could reach them rather than add extensions or modify their gauge.