I had a similar issue with a valve extended installed on my 2011 Sunseeker. I purchased a Pressure Pro tire sensor system and installed the sensors directly on the metal stems, no extenders used. I have been using these for 3 years now no problems, I set the tire pressure in the spring on my first trip and have not had to add air for the summer and fall. I do remove them in the winter.
We had the Big Foot Automatic system added by the factory when we purchased our 2011 Sunseeker 2650DS purchased from RV Direct in Albany NY, I believe it was a $2600.00 adder? Works great. I understand that you need to be careful when doing this manually not to twist the frame of the chassis?