I both drove with Neko from Vancouver to Fort Collins Colorado and back, and flew down with her. The drive was 3 days each way. I originally thought it would be a nightmare, as Neko made noises on the 10 minutes trip to the vet. I gave her Rescue Remedy for Pets and sprayed her carrier with Feliway. Once she realized she wasn't going to the vet (little did she know!), she calmed down. After that one long trip, we were able to take her on other trips with us, car and ferry rides. All times staying in pet friendly hotels. Her last trip she was taking quite a few medications as well as insulin, and I had to give fluids too. That time I also had to give her PMPS dinner and shot while in the ferry line up on the way there, and on the ferry itself on the way back. Cats can surprise you. Some practice trips before hand might help. Neko was better with the carrier door open so she could get out, but she mostly stayed in there during the car trip.
The flight was more interesting. Next time I wouldn't plan a trip that was so close to the US Thanksgiving.

I used the
Kitty Holster for that trip, and it acted a bit like a Thundershirt and she was quite calm on that trip. Plus it was easy to put on and stayed on until I wanted it off.
What dose you give a cat depends on several things. If flying and not able to monitor as closely, I might give a smaller dose. Though I didn't - I knew I'd be a place I could test by nadir time so gave full dose. Car trips also depends on whether you think he will eat in the car (good thing to try before hand). Neko would only eat if we stopped, so when we had food or stopped for gas. I didn't want to do tests while DH was driving, so we stopped for those anyway. On the way back from Colorado, where she had SRT, she was on a bit of a roll down dose, so I gave her a bit of a reduction to help keep her safe. Going through Wyoming, all the road stops were closed! And we arrived late to one of my planned test spots in Washington due to traffic jam from a fire (some idiot tossed a cigarette onto the dry median). In other words, plan for things to not work exactly as you want them to.