We just traveled with Tiggy -- about 8.5 hours Monday and again on Wednesday.
We had a collar and tag on him and let him loose in the car while we were driving.
His cage door was open, and we have food and water set up on a placemat and a litterbox.
He was mostly either in his cage on the bed or laying by the food.
On Monday, we gave his regular food and shot in the morning -- and started our trip at +7
by the time we got to the hotel at +15.5, he was over 300. (we did not stop to test and shoot at his regular time)
On Wednesday, he was a bit low in the morning, so he got a half dose. We left the hotel at +2 and got home at +10 or so.
At shot time, he was at 180.
In the car, he doesn't eat as much as usual and he doesn't exercise as much as usual.