The bulkhead mounted one from USGlobalSat is meant for exterior mounting.
(That's a scary looking place for a propane cylinder by the way Val. Looks like a leak would go right inside.)
You've think so, and there are plans to move it aft or to box it in place, but the truth is there's a sill you can't see and the deck camber is signficant, meaning gas would sink, roll "down" to the gunwhales, and then to the scuppers.
The fact is, it's rarely on, and I have a propane sniffer in the engine room from my Atomic 4 days.