The small propane cylinders can be removed from the H2o heater and gas grill when finished using. But it is illegal in most areas to store them anywhere in the cabins. You also should not store them in cockpit lockers if not equipped with the correct bottom vent.
Even when detached from an appliance, they can still leak propane, as hellosailor mentioned in the above post. Some boaters store their unattached cylinders in a specially designed nylon bag with a bottom mesh fabric, hung from the stern railing.
True Blue . . .
sold the Nauticat