Thank you for all your answers!
JamesL - this has crossed my mind - it is not a bad idea! I was thinking, though, about the lens getting dirty all the time...
I will explore the Garmin range - there are tow types there, I just need to check a couple of things.
They are not much bigger than the one I have. And the advantage of mine is that the bracket stays with the wire in the bracket and the unit itself is easy to remove. It just has the wire socket in the wrong place...