Hi DD,
Sorry for delay in replying - got sent on a course for a week. I drilled the rear panel of my van, with my heart in mouth!! Used loads of mastic in the hole after the job was done and there is no evidence of any water ingress.
The 7" display I use is on the dash,located in the passengers corner, and is removable with a simple wing nut, although the bracket stays there(sticky thingy). But I do find that the display is too large. Perhaps with a 5" a central location maybe better. In my Sorento with sat nav in, there's no room.
Looking at cameras that are available, there are ones with two lenses in, one for close view and one for distance, but they are comparatively expensive. I find the view with the lens fitted to mine as perfectly ok for rear view when reversing, and for vehicles approaching to overtake. Its all in the set up!
I can't get too excited at running the cable/s in the awning channel. I think that the maybe prone to damage there when brushing up against bushes etc.