So my hands aren't small enough to reach thru the outside dual to get the valve caps off the inside dual to check pressures.

Does anyone use the extensions that fasten onto the outside dual once installed? Do they work well, or should I just get my kid (or wife) to take the stem caps off when I need to check the tires?

That assumes a long gauge and chuck can be manipulated to finish things once the caps are off.

Are there any brands of 17.5 wheels that dont have this problem due to a larger opening? When I had a trailer with 16"s I was able to reach thru, but not on these 17.5s.

Extensions leak. Use this on your compressor. Snaps on with no hands. Releases with one button . Works great.

JACO Lightning T-Series Tire Air Chuck - 1/4" F-NPT (Open Flow) https://a.co/d/0Ao4yrR

Flow through valve stem caps may be what you're looking for. And depending on angle of the inner valve stem, milton makes a bent shaft dual head service gauge that may work to get a good seal to check the pressures.

Leaks are why I left the extensions on the shelf at the trailer supply shop and ran here for your confirmation. Thanks.

When I get a kid to the farm to undo the caps I'll see if I need one of these. Thanks.

Have the same problem on my trailer. Use a 3/8 ratchet extension, with I think it was a 3/8 twelve point socket. Fit just right to take off the cap.