Nice to have the Tire Man solution, but not necessary. I used plastic extenders that came with our used MH until I got new tires. I asked Costco to put longer valve stems on the outers so I could reach them with my pressure gauge:

No problem with the inners. No extensions needed. I actually put regular valve caps on to keep dirt out and use BruceMc's hose or tube tool to put them on and take them off the inners (link in his post above). I can reach the outers with my fingers.
Now I'm just worried about j-d's warning about plastic valve stems. Costco only has plastic ones. Tires cost way more elsewhere. But no problems in 7 years, except one time when I tried metal extenders and one failed to close after I checked pressures at a rest stop. I will start looking for metal valve stems for the next time I get new tires.