The section relating to subsidiaries explains itself.
The section Vehicle security is somewhat more complex as you will need to give the correct answers, if you fail to do this the application will be returned causing delays.
For rear doors the Border agency like to see locks of an acceptable standard,a padlock can be opened in 2 seconds by the criminals roaming around the ports.
Seals can be used to secure the vehicle, they need to be of a good quality, keep in mind that seals can be cut and glued back together in a manner that is difficult to detect by the driver, especially if he does his checks in the dark.
Steel wire seals are the best solution this does mean that you will have to provide wirecutters to your drivers.