ABYC, NFPA and NMMA prohibit manual valves within accomodation spaces or indeed any connections, joints or juctions other than at the appliance.My P323 has only one tank plumbed. The other is merely storage for the spare tank. The port tank has a copper line coming from the top out the propane compartment right through to the galley behind the oven. There is a manual shutoff behind the oven.
The original setup had some sort of antiquated liquid leak detector attached aft of the regulator before leaving the propane compartment. Last year I had a modern (Trident) solonoid switch installed in place of the leak detector.
Also, bear in mind that my vessell is hull #2. I have learned that many improvemnts were made along the way.
Propane is a very safe fuel if installed properly. Installation is not rocket science but if you do not have access to ABYC or NFPA standards its better left to someone who knows how not to blow themselves up