YANBU. Ok, you've had lots of recommendations for curing travel sickness. I bet you've tried most of them. You still have a child who gets very carsick, right?
(I do get that medicating doesn't always work either, or has consequences. I still get travel sick as an adult, although not as often as when i was a child, luckily. Usually the choice for me is between risking feeling and being very sick on the journey, or arriving for work meetings and interviews having taken the tablets and feeling absolutely exhausted. It just isn't fun).
Adults who enjoyed driving pre-dc and like doing long journeys often seem to insist on carting small children on long trips for no good reason. It's tedious and selfish and I agree with previous poster, it's often about finding child oriented activities boring and wanting 'quality' trips for the adults. Nothing wrong with trying to do both IF YOU CAN but dragging a travelsick child around for no good reason is selfish.
Is this very long Euro trip you husband wants to do just a holiday? Tell him not to be an arse. The world won't end if he doesn't get a foreign break. If it is for much needed medical treatment or to see an important relative who cannot travel themselves, ok, then go and do the best you can. If not then forget it.
I can still remember what became unhappiness and then fear about car journeys from when i was small. I hated the feeling of constant nausea and i could tell how frustrated my parents were at me. They also got more upset snd frustrated with me the more they tried to manage the problem, when that didn't work ('what do you MEAN you're feeling sick again, we just stopped for 20 minutes, you said you felt better, we're never going to get there ar this rate - oh for god's sake, she's been sick again, pull over... were you looking out of the window? Were you? I said we shouldn't have let her eat lunch!' and so on and on).
If you don't have to do something which makes a child sick, then don't.