They pass by customs every time because they don't have the clearance to enter the Engineroom.
While I'll be the first to admit there are any number of hiding places aboard a submarine, it's good to know the following:
- All those above you in the chain of command were once junior people, too, and likely collectively know all these places.
- Regardless of how good a hiding place is, the more hiding places are used, the greater the likelihood some Chief is going to stumble across one of them.
- The CO who authorized the use of one of the torpedo tubes to store all the booze was dead serious when he made the 1MC announcement that if any booze was found anywhere else aboard ship, there would be a water slug shot from that tube.
That said, nobody ever disassembled the CRDM Current Reading Shunt Box to see if anybody had stored a bubble wrapped bottle of Bicardi Reserve inside.