Unlock the trunk, and methodically remove the weatherstrip that used to surround the opening. Next, clean all traces of the old adhesive used on the weatherstrip mounting area. Next, place the new weatherstrip in position and cut it to length, leaving 1 or 2 inches longer at one end. Put a bead of adhesive around the entire weatherstrip mounting area and fit the weatherstrip to the body opening, with the joint to the rear. Lastly, close the trunk lid and leave it closing until the adhesive has dried in part at least.