Let's make sure we use the right terminology, "extensions" are cheap accessory things that screw onto the existing rubber valve stems so that you can check pressure and add air with "beauty discs" in place. They tend to unscrew and leak and can cause rubber valve stems to crack and leak from vibration causing tire failure from under-inflation and collateral damage to underside parts of RV. Having long custom formed SOLID brass or steel valve stems installed, using Borg or Tireman, or custom made ones from a truck tire store, is the safe and reliable approach costing up to $200 parts and labor. Checking air will be easy with no need for gymnastics and cussing as you release air instead of adding it.