My experience jft, differs greatly. We had a double 10lb cylinder propane locker on our last boat, but used the disp. bottles for the stern rail-mounted Magma - since the propane locker was midships and usually too much hassle to connect the hose.
We also removed the small bottles after each use. But the occasional unit developed a leak - not enough to make a loud hiss, but if placed close to your ear, there was a slight hisss. Our slipmate, who we cruised with regularly, kept his bottle attached to the Magma - said it's safer keeping the leaky bottles in open air than in his vented lazerette.
True Blue . . .
sold the Nauticat