I made up a sleeve, using some thin wetsuit neoprene, that fits tightly around the cable and just hooks over the charge port cover. Rain doesn't seem to be a problem, but I found with my last two cars that snow very definitely can be. When snow gets packed around the open charge port it makes life a bit difficult, but other than being a nuisance to clear, it didn't cause any problems with charging.
I believe there's a commercial version around, that uses magnetic strip to hold the larger end of the sleeve to the bodywork of the car, but can't find a link to it right now.