"Richard Russell" wrote
Is there such a thing as a flexible Schrader valve extension which could
be left permanently attached to provide more convenient access? It would
need to be at least 6" long.

any truck parts supplier will sell them, also motorhome type places,
commonly used as tyre valve extensions, where you have dual rear wheels, and
thus have an awkward job getting the airline connector onto the tyres
valves,

you can also get spare tyre valve extensions, mainly for motorhomes that
have the spare tyre under the chassis as most vans do, but then have a low
hanging body built on the chassis making crawling under to check the spares
pressure a bit of a chore,