I want to fit a 13 pin plug to me l200 56 plate i already have a 7 pin but sometime tow my father in law caravan which is 13 pin

We bought a crap adaptor for the trip which was shite to say the least.
So am wantin to fit a 13 pin and keep the 7 pin on the other side for my caravan

Is there any wiring buffs local to crewe in cheshire who wants wire me 1 in will pay.