This might be a stupid question, but... where do I have to put the file ? It's not a vehicle or a map so the wiki doesn't inform me
put it in the objects folder in your game directory. then go into the level editor, and add in the file.
Judging by the pictures, it might be easy to drive off of the course. - - - Updated - - - Where is the objects folder?
Anywhere in the games whole sub-directory, just remember where you put it, then open BNG and load a level, then you have to use the world editor (F11).