I've used an extension on the inside wheel for the past 10 years without issue. I replaced one of them once over that time, I forget why. Pretty painless.
Every time we stop at a rest stop I put a hand on each tire to make sure they're not low and over heating. Never had a flat on the road in any motorhome, or truck RV.
You need one of those front and back angle air chucks and gauge to check and fill the outside tire.
I would think with alloy wheels they have longer valve stems to provide access, no?
These are the cheap ones I've used (inside duals only) that leak....LOL