On the front, the wheels are installed "dished in" and the valve stems are visible and accessible from the outside.
On the rear, the wheels are installed "dished away from each other" and the valve stems are trapped between the wheels.
Access to both requires reaching in through the hand hole and fiddling with the caps, then fishing the dually chuck in there to check pressures/add air. An extension on one only solves half the problem. A straight extension only helps with the inner dual.
It does nothing to help with the outer, harder to access, valve stem.