As indicated by JP_Finn, you have to find a suitable rock (one that doesn't require climbing, or at least doesn't require impossible climbing), and it can take some searching to find one. Unless you're attempting this in the hottest part of the summer, I'd recommend using a raft or punt to get to the skerry in order not to get cooled down by the water as you're going to get cold from being naked. You COULD wade/swim out there in good time and heat up to a reasonable temperature while clothed and then only strip as the time approaches. If so, bring food and something to craft while waiting for the strip time.