Hi Lolly,
First time that i have replied to one of your questions,
I have fitted two of these external tv connections, on my last and present van.
Our Bailey Ranger 460/4 fixed bed with the telly located above the worksurface , so that you can watch either in the seating area or in bed.
For this reason I fitted the external aerial connection quite high up the side of the wall, so that you can insert the external cable whilst standing.
I have a external TV mast which I clamp to the jockey wheel.
You should get a carboard templet showing the positions of the four fixing screw holes and the large hole where the internal tv cable connected to bracket that you are fixing.
I found out that if you ignore the templete drill the large hole first ,position the external brkt within the hole you can then mark out the four smaller holes, the carboard templete on the two brkts that I bought showed the holes to near the large one
Trust this all makes sence
Royston