I would go the middle "X", you will find it gives a good coverage whether you have a reversing 120 deg cam or a rear view 90 deg cam, if you check the rear lights wiring loom you may find a live 12v cable there to give the cam a feed, makes for a shorter power run for it then just run the vid wire back to the tug.... I think the light feeds from the right hand side usually, if you have a cupboard in that spot I would just feed it straight thru the wall into the cupboard then down thru the floor and underneath up to the tug........... sometimes they pre wire but can be a bugga job finding it. My rear cams are on all the time as a rear view, works very well for those that hide behind you.