Shipping Containers are metal boxes with doors for carrying cargo, and they are not in themselves items of high security.
When being used for shipping cargo, the container is fitted with a customs seal when loading is completed and it is after that while loaded, transported from secure compound to secure compound or onto the ship. The Custom seal is an unthreaded bolt that has a number and or a barcode. This is fitted into the door handle and passed through the customs catch when the door is finally closed. This number is recorded on the shipping notes and it must be that number on the bolt when passing through and arriving at the destination. If it is broken or exchanged for another number, the customs officers will know the container has been opened, and investigation will take place.
So when using a container for storage outside of that environment, we need to have better security, so we fit “lock-Boxes“. These are heavy gauge welded steel covers to protect a “shutter “ or “c” padlock, and it can only be accessed from the underside
The Lock-box is welded to the opening right-hand door and the staple is welded to the left-hand door. (Shipping Containers are designed always to have the right-hand door opening first but that can actually be reversed)
When the doors are closed the lock-box (which has a hole large enough to pass over the top ofthe staple) passes over the staple.
The shutter padlock is passed up inside the lock-box with the lock pin open.
The Lock pin is located through the staple and is pushed shut.
The key is turned and removed leaving the padlock pin closed into the staple, and the padlock is retained inside the lockbox protected from the weather and casual thieves.
The lock Box offers excellent protection, and delays access to villains but are not 100% protection against the most determined robber.
For good quality, Shutter Padlocks see https://www.cisapadlocks.com/ there are several sizes, and your container supplier will offer to supply or advise you of the size you require that is best suited to your Lock-Box.