[DutchmenSport]

If the water line is exposed under the slide out going to the refrigerator, yes it can and does freeze.

This is my line going to the refrigerator at the outside edge of the slide-out, underneath, 100% exposed:



This is the other end where it goes inside the frame (where it is heated):



This is where the line comes up through the slide out floor (inside the camper).



So yes, if water sits in that exposed section under the slide out, it will freeze, unless you can keep a steady stream of water trickling through it, which isn't possible with a refrigerator ice machine.