Hello, we did a car trip when DD was 5-6 weeks old. It was only a (long) day of travelling but we did another much bigger car trip when she was 6 months old and the same principles applied:

It is much easier to travel if you are breastfeeding, you can stop anywhere anytime to feed that suits (bit harder I imagine to mix up formula on the side of the highway)! Bring your own equipment (we took a portacot and sheets cos the ones the motels supply are sometimes on the dodgy side) and the other big tip is allow a lot more travelling time. If you need to stop to feed or change or settle, it takes a lot longer sometimes than the usual 15-30 mins that you allocate for a rest stop!

Good luck, I hope you enjoy your trip and all the best with your TTC journey!
:-)