My propane tank on my Morgan 33 O.I. is located inside a custom made, plywood compartment situated in the aft, port compartment. There are two valves on the tank, one electronic that is connected to a sniffer, and the standard, manual valve. The tank has been there for more than 20 years with no problems of any kind--ever. It is protected from the elements, rust free, and the line to the stove is easily accessed and checked periodically. I only turn it on for cooking, and as soon as the meals have been prepared, both valves are turned off. The hatch opening to the aft, port compartment is a bit too narrow to accommodate the tank diameter, but only by 1/2-inch. Therefore, a bit of work with a jig-saw quickly provided easy access, without causing any structural problems.
I'll try and shoot some photos of the tank box when I go back to the boat on Thursday.