Very neat Andy, coincidentally I am in the middle of fitting mine right now.
I have to choose the position of camera to give the best view. Short of connecting it up and feeding it through the rear sky light temporarily, is there any optimum position to calculate--or suck it and see?
Also how do connect a warning buzzer to the indicator circuit? I have a Maplins one but am having trouble deciding where to take the feed from. Hazard unit?