if its the same as my 2015 there is a space next to the cigar lighter for another socket? I fitted another good quality socket with waterproof cover, maplins sell them, and just omitted the cover
you need to get a live feed from the fusebox to the right of the steering wheel
there is a couple of thick red wires that feed the fusebox sticking out of the front
i stripped back some of the insulation and soldered a wire around it then use self amalgamating tape to insulate the joint and you need to fit a fuse as close as possible to the joint to run your wire off, fuse sizes depends on what wire your using but nothing over 15 amps should be used on the socket anyway which should cover a decent tyre pump or cool box etc
the ov (negative) can be taken from the existing cigar lighter