I assume you are heading south on 81? If so take I-66 to Marshall, then 17/15 south past Warrenton to Opal then 17 to Fredericksburg. It is 4 lanes and traffic isn't an issue until you get close to Fredericksburg.
You could also take I-66 to Gainesville then Rt. 234 to Dumfries then I-95 south. Both are routes I've towed on many times. Both are good for towing and both are worse during rush hour.
Wright and Penny
2010 Tundra 4X4 5.7L V8
2014 Rockwood 2604WS
Life is a cruel teacher. She gives the test first; the lesson then follows.