Disconnecting trailer lights is not so much for protection from shorts as it is from cold water striking a hot bulb which is what destroys lights. I always disconnect and I can't tell you the last time I replaced a trailer bulb. If you look at trailer lights from the bottom, some are wide open. The idea being that if you took a water glass and tipped it upside down into a bucket of water it will trap a air at the top. If the lamp is supposedly sealed (but not tightly) it can leak water into it until it reaches the bulb and then it pops. I've seen lots of trailers with one or more lights half full of water.