Same here, I have one on my Plus 4, the wife loves it as she is a bit on the short side and it gives her somewhere to rest her feet. I do keep documents in it, but mainly those I don't normally need such as a copy of the MOT, insurance, V5, circuit diagram, and anything else needed when out of the UK. Even has enough space for an electric tyre pump. Tools and spares are in another lockable box under the bonnet.
Like Mike, we find it indispensable when touring in Europe.
It's an ideal place to keep documents but also to store camera, sat nav and other bulky valuable stuff when leaving the car unattended.
Ours is covered in a thick layer of black neoprene. This makes invisible to the casual observer and also makes it much more comfortable to rest feet on.
Niall
