I have found that the investment in Dually Valve Stems
was well worth the money.
Depending where you are there may be a distributor in your area, or you can call Dually direct and they will ship to you.
The inside valve stems are there. As Richard said, small hands may find them easier. Also use a strong flashlight and look through each hole and you may see it.
You will need a truckers air chuck and gauge. It will be a long stem with a double head with one head being about 45 degrees offset. The idea is to put the 45 degree end through the hole and pull backward on the valve stem to fill it. With the Dually valve stems they will all be on the outside and accessible.
I have a 2015 Tour 42qd, a sister to yours.
p.s., typically the valve stems on dually's will be 180 degrees offset, give or take a couple rim holes.