It works! Ah. almost
You may put a gun into trap cantainer! But there is a problem - trap containers repeats animation of opening and closure non-stop, even when the gun inside was firing at my sub. Unfortunately I dont know where is it, and how to slow it down/

Another problem is that merchant ships doesn't support armed loadout - guns will be added to all merhant ships of a cirtain class if you rearm them without considering of their cargo