The first thing to do is to make sure the caravan is level.  (If you use the spirit level to level the socket on a sloping caravan, you will have a skewed socket when the caravan is level).

Next, determine the location of the socket. You will find that the internal fittings of the caravan will influence this decision.

Also bear in mind you might change from a full to a porch awning.

Remove any furniture that is in the way so you have easy access.

Try to locate the position of the socket close to a natural join in the internal wall.  (This in my view is imperative, as you need to slide the wooden frame between the external skin of the caravan and the internal wall, and easy access is essential).

Place the wooden frame where it is most convenient and measure its location against fixed objects (in this case windows frames) to judge what impact the location will have on the outside of the caravan. (Will the socket location obscure logos reflectors etc).

Working from the inside of the

caravan, drill a hole from the

inside corner of the wooden frame
to determine (from the outside) the

corner of the square hole that will

be cut in the caravan skin

From the outside of the caravan place your template so that the drilled hole is in the same corner as the wooden block.

Using the spirit level, level the template and tape in place.  Pencil line the internal edges.  Mark the screw holes.
Remove the template and mask up the outside the cut line. (If you don’t mask up, the jig-saw will mark the paintwork.)

Drill pilot holes in each of the three remaining corners.  Using a bit large enough to accommodate the jig-saw blade, over drill the pilot holes.