FWIW, what's described above is the reason I always leave the main propane valve turned ON - when in storage, when on the road, and when parked/camped.
That valve seams to me to be a bit too fragile for much total use over it's lifetime. Of course I would shut if off when required by law in certain tunnels and when on certain vehicle ferries.
Working on propane tanks is complex, as I just had it done on our RV. The main fill valve had a micro-leak from it's screw-in threads for years - probably since when new. The repair shop had to burn-off a nearly full tank of propane for a couple of days to empty it and then remove the tank from the RV to remove the fill valve with it's stripped threads. The shop technician said that those fill vvalves are probably screwed-in by machine during manufacture of the tank and that stripping of the threads can result.