On long trip, we crate our pups...for safety reasons. But on short car rides, they own the back seat. Boscoe (5yo Cardi) get super excited. He loves the rides too much! He knows we're going somewhere fun...dog park, hiking trails, even the vet's office! But whenever the car stops at a red light or stop sign, he barks like nothing else and calms down once we start moving again. Oh and the radio has to be on and slightly loud too.
I know this doesn't help...but just thought I'd contribute.
Range used to just go crazy, jumping from back seat to front seat and on me. I thought it was just because he was a puppy, but as he got older he just became unbearable to drive around, so... solution, a crate. At first he hated the crate and would have anxiety in there, because he was never crate trained to begin with. But then I started to train him that it was okay to hang out in the crate, by giving him a treat every time he just stepped in the Crate. Then I started shutting the door and would feed him treats. So then having him go in crate in my car was a lot easier too. Now he just sleeps in there and can go as long as 3 hour drives sleeping the whole time in the crate. He only whines when he knows we've stopped.
When we had our older Corgi he hated the car, and would dribble as soon as he was put in there, so we never persevered with it, have made a concious decision not to do that with our 2 new babies and will take them out in the car daily.
I would try making very short trips and reward for getting in, and getting out of the car, Take them to fun places instead of just the vet, as it maybe the destination as opposed to the journey that makes them anxious.
I agree with the pet bed. Worked like a charm for my Ladygirl -- after she stole it from my mom's Corgi who was in the car at the same time!! LOL!! Also, if you have leather seats -- ruh-roh!!!! This was a big point of contention for Ladygirl. She hated the "squeaking" and "sliding" all over the place, so I put her favorite blankey in the back seat to help keep the noise level down to a minimum, her bed on top, and everything's fine. She really wanted to be up front with me, in my lap, head out the window before I discovered what it would take to calm her down.