Thank you for the replies
Thanks to all of you for the replies. I have indeed capped the fittings with 1/2 brass plugs. Mission accomplished. The concern was not over the fact that the outside shower was a concern during winterization, but rather during the winter usage with water in the system. I have removed the fixture and filled the shower box with insulation. Interestingly enough, the wheel wells have no insulation and are only a few inches below the shower box. Probably just made myself feel better with no real logical reason! However, when I sleep in sub-zero temps, I open the cabinet doors and use the furnace for heat. So maybe every little bit of insulation I add is of some value.
Just as a side note, I don't use anti-freeze in my system at all. For two winters now, I have successfully blown out my lines by running air through the pipes for about two hours at 30PSI but with a lot of volume. (all faucets open) Because I use the trailer so much, I end up winterizing at least 6 to 8 times per year and really don't want to deal with the antifreeze. Between usages, I often see sub-zero temps and so far, have had no problems. I do have to run the pump off and on during the line blowing process to ensure that it is emptied of water as well. I usually pause the process several times and even repeat the process as necessary to get nothing but air coming out of the lines. (I hold my hand in front of every faucet to check to see if there is any moisture in the escaping air. I do the same at the low point valves on the bottom of the trailer.) I'm not recommending this to others because I believe this works well, partially due to the very dry climate here in the mountains.
Thanks again to all of you and safe travels.