Here is a link to a waterproof exterior TV cable connector: http://tweetys.com/cabletvplatepolarwhite.aspx
If your trailer came with a factory-installed exterior hanger for a portable barbeque grill, you might find a simple way to hang your TV from that hanger. But I gotta admit, that exterior hanger from Thule looks way cool.
Good luck on finding a path from your existing TV cable connections to a location where you plan to install your new exterior cable connection. Let us know how you do it--and whether you lost your sanity and/or your religion in the process!