We have our 2014 3850RL and had the fresh water freeze up twice so far. Exactly the same as yours. Only, the second time it happened I sent an email to my dealer and to Trilogy. Long story short... After two days of work at my dealer and a night in a motel, I have the Trilogy back, it is in the low 20's as I write this and all is well. My dealer did a lot of work to include relocating the pump, isolating it from the frame where it was mounted, adding insulation to the plumbing and sealing up air intrusions to the underbelly. Will post some pics in a few days.
Bottom line, notify John Armstrong and your dealer and tell them you want it fixed. They made it happen.