Zenhussy,
Ever try ginger? It is suppose to relieve nausea in dogs for motion sickness and it natural. I am not saying that they pills from your vet won't work either, but I think the ginger would have less side effects. Kinda like Draminine... that stuff makes me almost unconscious when I use it. Kinda defeats the purpose of trying to relieve the sickness.
While I do not know how much to give I am sure that your vet or a website could give you the proper dosage.
I know that this is a puppy thing, but I have heard that putting a ticking clock in the crate would calm them down. I had a friend with a lab that it worked perfectly with.
I hope that some of this advice works and I hope that your travel experience is a good one.

Jessica

"Take these chances. Place them in a box until a quieter time..." ~DMB