My 2019 19ERD has no waterline under the floor. There is a drain pipe under the freshwater tank and 2 drain pipes under the kitchen. During winter I let the freshwater tank drain and the water-heater drain open. Winterize by sucking in 1,5 gal of pink stuff until it comes out on all faucets. Then open slightly the two drainpipes under the kitchen until pink, then close them. Here in Quebec temperatures drop often below 0 deg F. Never had a leaking waterline. I wouldn't rely on a foam insulation to protect a waterline from freezing.