I had occasion to be inside the "vault" at a shop that had formerly been in the b-w business (they stopped year ago, so I an not going to retroactively criticize them now, besides I do not know how they treated 'customers'. It was no longer in that business when I visited, but they still had some stuff they took in before they exited.
Their ad for vault services included a photo or high quality artistic rendering of a bank vault sized door and advertised "vault services". The actual "vault" was a locked room, including a locked door directly to the exterior of the building. The interred guns were sitting on shelves, not in safes or vaults. Nice setup for someone to pull a job, plus locking the door would probably qualify as "non-negligent" care under bailment law.