I have a 2017 Whitehawk and have no problem camping in weather down to about 25 degrees. Our underside is covered in black plastic. I used a Camco heated hose, just like Rustic Eagle, but every campground I've stayed in requires that you disconnect city water if temperatures drops below freezing. The one thing I did do after our first "cold" trip was go plug all of the openings into the interior. For example, in the bathroom closet the vent pipe ran through the closet, there was no insulation around the pipe where it passed through, and that part was open to the outside kitchen. Never had a problem with any of my water lines freezing.
2019 Chevy express 2500 Van Coversion. 2017 Jayco 23MRB: 26' total and Glacier Package. 2 Renogy solar panels. Married 46 years. Haley the mutt, 3 years old. "Excited to learn new things everyday and humbled by those who offer to help."