Invest in a car seat! They really make trips better. I've routinely traveled across the state on a monthly basis, with ZoE, to visit my kids at college. ZoE knows the seat is hers, she knows right where she's supposed to go in the car, and she travels well there, plus being boosted up, she can see out the windows.
I take food and water for the trip in travel containers. I stop every couple of hours to see if she needs to go potty. ZoE is potty pad trained, but now that shes older, she will go outside if need be. When she was a puppy, she would only potty on pads, so I would lay them on the ground outside. When it was raining, I had to put the pads in the trunk of my car (mustang back then) and hold the hatch open to protect ZoE from the rain.
Here's a pic of ZoE in the backseat if my caddy.
__________________ (ZoE  )(Chelsea ) |