Personally I'd create a solution which had zero joints and connections outside, to avoid problems caused by ingress of rain, snow, etc. My solution would be one continuous mains cable from the 13A socket to inside the car. Before you do that, check that you can shut the cable through the door seal - should be fine. 986 had a cutout in the door seal for cables, can't remember if the 987 had too, but the seal is pretty flexible and can manage most normal cables. If you can't find a manufactured lead long enough, just buy some appropriate cable and put a plug and trailing socket on it. Plug the CTEK into it inside the car, position the CTEK where you can see the lights. On the 987, the CTEK should work fine plugged into the footwell power socket, but to be sure, check it is still live say an hour after you have locked the car. Some sockets are programmed to turn off after about 20 mins (that's a whole world of Porsche in itself).
