I also play by this honour rule, not loading external reserves unless the seas are reasonably still. My last patrol I came back to port with my stern external reserve still in its canister, as the weather was miserable all the way back to port. I've never been jumped yet while moving externals, but other players have reported that if they are jumped, they consider this torpedo abandoned in the haste to dive and make a point of not using it.
External torpedoes were stored below the deck plates in a watertight tube. The normal practice was to wait until the boat was in an area where they weren't likely to be surprised by an aircraft or enemy vessel. As shown in the photos above, it required a type of winch to be erected. In the game, you cannot move your stern external torpedo to the bow, or vice versa, but in real life they could; by tying flotation vests to the torpedo and tying lines to it, it could be floated fore or aft and then taken inside.
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