… but the problem is getting the cart to the location and back home without the water freezing.
Okay, it’s not THAT cold in TN. We used to live there for several years (Chattanooga area and Whitwell… outside of Jasper & South Pittsburg). You shouldn’t have a problem with your water lines freezing up during the day, just overnight. The tanks will stay thawed just from the motion of the water sloshing around. The lines should all be inside your trailer. For overnights, I would do to the cart what we did to the RV when we stayed over the winter in Elizabethton (outside of Johnson City)… Heat tape and pipe insulation! If you do use heat tape and pipe insulation… figure a size larger than your pipe to allow for the heat tape (we use Frost King brand).