Hello rear lights hole, easy fix, sealant or buy the genuine plastic thing tailgate-towords the top right of the tailgate is the tailgate wires which run through the rubber, this has probably come off, clean up and reattach and use some silicone sealant and let it set. check your rear washer wiper pipe, the one that joins the roof to the tailgate (pipe) your windows misted up all the time ? spray some water over the tailgate and get a friend to jump in the boot ! listen for the water drops doors and sills, there are drian holes on the tailgate and doors and sills, they probably need cleaning, if water does come in then it can run out