Wherever you located it I would HIGHLY recommend it being outside and never in an unventilated, enclosed space (like the lazarette). Most seem to mount their tank(s) to the boom gallows or stern pulpit. I have a ventilated teak locker just aft of the mast that hold two 20lb tanks. A flexible hose is routed from the propane locker, alongside the companionway hatch inside the turtledeck. It exits at the turtledeck opening and enters the cabin via a bronze right angle 'through hull' fitting embedded in the cabin top directly into the cabinet above the icebox.  A second flexible hose then runs from the cabinet, along side the hull and aft in the locker behind the stove. It exits the locker behind the stove to attach to the stove.

I would also highly recommend an LPG gas detector/alarm. Some 3rd world countries (not sure about Mexico) do not add the 'propane smell' causing their propane to be completely odorless. An acquaintance was killed when like a bomb, a propane leak literally blew him and the deck off his boat when he got up in the morning and lit the stove.

Our first 42 (factory finish) (Ocarina, Tralfamadore now Blue Fin) had a sealed stern compartment with large round brass hatch cover and overboard spill port.   But it also had a deck box built over the top of the sealed LPG compartment.

Our second 42 (Sundowner, now "She'll Be Apples") was not a factory finished boat, almost though, and it too has the same LPG compartment and hatch found on our first boat..

We carried/carry two 20lb(9kg) steel.

I'd make a stern deck box, there should be pictures of Blue Fin on the net, if not I can post some.  Any gas leak will spill over the boat from the deck hawse pipes or drains athwart the cockpit. Of course you could always make the stern box gas tight and have it's own dedicated spillway aft, problem with that would be how high that spillway would be given the toe rail.

Construction Manual, Section 4-G-3 has a deck box mounted in front of main hatch. IMHO running the gas line as described looks interesting :|.   Those look like 10lb/3.5kg horizontal.

Scott West wrote:

But it also had a deck box built over the top of the sealed LPG compartment.

Of course you could always make the stern box gas tight and have it's own dedicated spillway aft,

Never NEVER keep propane cylinders in a 'sealed' or 'gas tight' enclosure/compartment. Any enclosure/compartment used to keep propane cylinders should be well ventilated (at the bottom of the enclosure as propane vapor is heavier than air)

Scott West wrote:

Mike McCoy wrote:

Scott West wrote:

But it also had a deck box built over the top of the sealed LPG compartment.

Of course you could always make the stern box gas tight and have it's own dedicated spillway aft,

I'm sure I'm misunderstanding you but just to be clear:

Never NEVER keep propane cylinders in a 'sealed' or 'gas tight' enclosure/compartment. Any enclosure/compartment used to keep propane cylinders should be well ventilated (at the bottom of the enclosure as propane vapor is heavier than air)

Seriously misunderstood/misread..

I certainly hoped so but when you use phrases like "built over the top of the sealed LPG compartment" and "make the stern box gas tight' it leaves room for interpretation (and not in a good way)