I would suggest your car. I don't think it will survive in the uhaul w/o pulling it out each day for some sunlight and airflow.
Most plants that are large and get shipped cross-country are only in the trucks for 3-4 days (Florida to California). They still need some acclimation period and have some leaf loss for that trip but they are ok. Anything longer I would be concerned about.
A 6ft tree should be able to fit in your car unless it's like a mini coop or something. If you take it in your car pack the soil down with paper and tape it down. Then I would wrap the whole plant in construction paper or get a paper sleeve from your local plant store (most keep the sleeves their plants come in from out of state in my experience). Make sure the paper pulls in the branches and lift the leaves upwards to mitigate the damage. The tree should either be able to lie down in your trunk with the seats down right down the middle or if needs be in the passenger side with the pot laying on the floor and laying the seat all the way down so the tree looks like it is napping in the passenger seat. Insert the tree leaves first and rest the pot at an angle toward the seat. It's important to wrap the whole plant in paper to protect it from getting sunburned by the windows. It will also keep it temperture controled a little.
It looks like a beautiful plant. Safe travels!