Many years ago I was given by my vet ACP tabs for my Westie, we gave them as prescribed, the dog went bazarre and started to go manic, I would never ever suggest those, not even sure if they prescribe them. The little dog was in the back of car which had those car rails in to stop him jumping over, he was biting them and they actually had teeth marks in the metal, we had to return home with him. I was later told they could have strange effects on some dogs.
When Jay was ill we were given valium to give him to relax him, I was quiet alarmed yet vet said they were often used on animals, its worrying when you are given medication and not sure how your dog will react.
I would certainly try the herbal remedy and maybe give it a try rum so to speak.
I also wanted to mention that you need to check what facilities there are at the ferry terminal for walking the dog, they was a story on a show in UK and some terminal will not allow them to walk while parked waiting to board.
Julie