As Turnup said forces have different levels of security.
I believe that it is recommended that the box is secured with a small lock and chain to prevent anyone picking it up and taking it away. The days of being able to chuck it out of the window in case of fire have gone.
I don't think they like the box kept in a wardrobe or cupboard.
It must not be above or adjacent to an exit in case of fire.Nor can it be stored under the stairs for the same reason.
They do like the box to be kept out of sight from visitors.
The best option is let them tell you what they want.
Regarding the anti-static mat. I don't think you need one. But, obviously, if you feel safer with one then it cannot do any harm. I wrote to the HSE as I was concerned about static caused by decanting blackpowder to and from plastic bottles. They said they did not consider this an issue and had no record of it causing any problems.