From memory the end cap is fastened on the the caravan body with just one or two screws, I can see one of them in your photo. There may well be a little plastic cap that fits over the head to conceal it. I don't think anything needs sealing.
Dave.
------------- Never argue with an idiot, they will drag you down to their level and beat you on experience.
Mark Twain.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.