Vans, reefers, intermodal containers, and other trucks and trailers often use barn doors, which are doors that open along hinges on the sides of the doorway. Barn doors usually use long locking rods that keep the doors securely closed at both the top and bottom of the doorway.
It is very important to make sure that these latches are engaged at both the top and bottom of the doorway. While it is easier to check the bottom than the top, the top can still be verified easily by taking a look up as you latch them.
Unsecure latches can lead to damage from vibration and even the failure of the locks to keep the doors closed. As you can probably imagine, failing doors are a big problem for a truck going down the road. Always double-check your door latches.