I took my TT into sub-freezing temps for the first time a couple of weeks ago. I took it to Truckee, near Lake Tahoe, CA. Forecast was for lows near 25, highs mid-30s. Based on some research, I thought I would be ok. Filled my fresh water tank, and plugged into electric only, with no hookups. Ran the furnace and electric heaters. We were toasty warm inside.
Everything was fine until about 11pm our first night, and then the water pump would not make a sound. We had no water for the remainder of our trip (2 days). I tried hooking up city water the next morning and night, and no luck.
The owner of the rv park said it was 9 degrees at the park in the morning. My phone app said it was 25 in Truckee. So, it could just have been too cold. But, something froze within 4 hours of arrival.
I am not sure where the water froze. All my lines are enclosed, except for the line from the fresh water tank. And the pump is enclosed, but close to the outside shower door, isolated from the rest of the TT. I suspect the pump lines froze.
When I got home (50/40 degrees), it took a couple days for the pump to start working again, and everything is fine now.
So, I would make sure any exposed lines are insulated/heated, and that heated air gets to your inside lines. (Although I have no proof that works yet. I hope to make some mods and try again this winter).
I hope relating my experience helps.
