Maybe I'm just too darn simple but I store my 1# propane bottles in the anchor locker, which drains overboard. Am I missing something?
No, you have it right. I've heard of anchor locker, PVC pipe holder attached to the rail or, as we do, keep it in the bbq grill which is attached to the stern rail - the key being to keep it outside the boat in the event of a leak. I ordered the caps because it looks like some good secondary insurance, plus will prevent the cannister from emptying out before the next bbq! I wish we had propane installed, but we don't, alcohol stove and Dickinson bbq on the rail with the portable tanks.