Thanks for the advice guys. I won't be using it a lot, just for the odd time so I can't really justify the cost of a roof one I'm afraid. I got one of the ones that goes on the back and it seems to do the job pretty well for what I need. I see what you mean about the rear wiper though, it seems to come on whenever you reverse and I have a bar that sits agains the window. Is there any way to stop it from coming on automatically? Thanks Dave