Have you tried a Calming Cap?
There are many calming supplements on the market, some have published studies behind them. You may have to try and see which one might help.
I also suggest to bridge the gap between trips around town and long trips. You wouldn’t go out and run a marathon without careful and deliberate training. Start with trips just a bit longer than your around town trips and gradually build on it. If you get “the hassles” you have asked for more than your dog can handle. Back up and reduce the distance. Then increase in smaller steps.
You could also talk with your vet about Dramamine. He may have motion sickness issues that only surface on long trips. Plus, the original Dramamine has a mild sedating effect.
Who knows, may be he has made some really bad experience on a long trip and you are dealing with an old trauma.
