in our coaches have to be re-certified every so often??

.

No

However, the newer fill valves and pressure relief device attached thereto are different. So, if anybody picks up a very old motorhome that has not been filled with LPG for many years, the tank might need to be purged and the valve assembly might need to be replaced.
http://www.propane101.com/safetyreliefvalve.htm

quote: A prudent man seeks the counsel of wise men!

https://www.barthmobile.com/eve...061/m/7543980367/p/1.