We've only traveled once with Maddie. When we took the 10 hour drive home from Ohio.
We only stopped twice. Once was to get food. I sat in the car while my mom ran into the subway to get us food. That was at the half way point, so she also went potty there. I made sure that I had a REALLY tight hold on the leash (I put my hand through it then wrapped it around my wrist a few times). and I also took her away from where all the people are. and I did a double check on her harness before I took her out of the car.
and we also stopped at a Red Roof Inn to stay over night. We never took her leash off, even when she was in the hotel room. We took the leash we brought, tied it to the one she was wearing, and tied her to the table. (we really didn't want to risk her running off again). When I brought her outside to go potty I picked her up, put her down outside, then picked her up and brought her back in. I didn't let her walk around much out doors.
and my friend lived right around the corner, so she came by the hotel room to visit me. I locked Maddie in the bathroom when she came in so Maddie couldn't take off.
and we also kept the "Do not disturb" sign on the door and kept the blinds closed so that the maid wouldn't come in.