Hi
Double electrics - dedicated wiring system ie: plugs into the wiring loom via passenger side rear light - standard wiring sockets for caravan.
I did think about buying a cheap splice in kit but was told that a dedicated kit simply plugs in. I have pulled the left rear hatch off the rear passenger side of my estate and the plugs are already there.
I was told maybe someone could tell me, that if I buy the dedicated supply leads that plug in the all is in the kit including relays if I need them.
Have looked under the car and on the net to check that the pre cut holes in the chassis are for the towbar and yes they seem to be, so maybe I have answered my own questions!
Fitting - yes I would have it fitted professionally for peace of mind but who makes £100 a hour max - I don't, if it were £50 then maybe I would consider for piece of mind.