IMO you will have to go farther south than that to dewinterize for making tour a of the USA.
Even here in northeast Oklahoma we have winter temps down as low as 30 below zero as a extreme. Most winters though its single digit temps 3-4 time a winter.
Your going to have to stay in the deep south like FL/GA/AL/MS southern TX/NM and AZ unless your set up with below freezing weather for your water needs.
Just about all campgrounds are closed. Many that are open have the water shut off.
I can't imagine touring the USA in the winter in a TT. You will sure have to be cold weather prepared.