Re: Coleman stove in the cockpit?
I've never witnessed one leaking "here and now". Did have adventures with a propane sniffer on one boat that insisted there was a leak, presumably from the box of propane bottles, but that was never resolved while I was around.
On the other hand, I had some propane and mapp bottles stored away at home in the back of a closet, and after maybe ten years the full bottles were empty--without ever being used. So I can tell you, THEY DO LEAK. The only question is how slowly or inconveniently.
You can address that by buying nicely made brass (sorry, not bronze) gasketed screw caps that are sold specifically for that purpose, sealing the bottles while they are in storage. Probably $5-10 each these days if you can chase them down.