Even with a TT and exposed grey/black tanks, you can travel in temps down to low 20s without problems IF you leave the furnace on and set at it's lowest setting around 50*. This does assume your water tank is inside the unit.
The coldest I've pulled my 30' TT back in the 90s was 15*. Roads were clear but the rest areas were solid ice from the snow being packed. Unlike some others that pulled off in cars, I knew to get slowed down to a crawl while still on the plowed off ramp.
At the first of the year, I would just plan on I40 to NM doubting that snow will be an issue. However, I would have a plan B. What may be more of a problem is having campgrounds closed along the way.
