That's difficult to say. Where the water lines are outside the trailer I supposed they could ice up, but would it cause damage? Hard to say. I did a good job of winterizing the trailer this year but forgot about the DW's truck (SUV) and the summer window washer fluid froze up and "popped" the water line, causing it to come apart at a connector. Fortunately no permanent damage was done to lines or the pump.
Now for the confession of stupidity (or more stupidity I should say), this past week I took apart the interior of the truck to track down where the leak was and reconnected the line (which goes to the rear window wiper). I used straight tap water to fill the reservoir to find the leak and it never crossed my mind to add fresh anti-freeze after the fix. Sure enough, the temperature dropped enough over night to freeze and pop the connection again, flooding the floor mats. The point of this little rant is that you might be surprised how easily an outside line could freeze overnight with pure water.
Unfortunately I'm not sure I would do anything different than you already have. Your pump and interior fixtures shouldnt freeze.
2011 F-150 5.0L with tow package