Road trip + car sick dog > Dramamine?

My dog isn't good in the car. It was very slow going in the beginning getting him used to the car and now he will willingly hop in and won't vomit. I don't feed him in the AM and our longest trip is 30 minutes before we take a break because he will dry heave if I drive too long. In the car, he just lays down with his face on the center console. He used to drool really bad and shake but now he only drools excessively if I leave him in the car while I run into a store real quick.

For our normal trips, I make sure a few windows are cracked, the car is nice and cool and not stuffy, the music isn't loud and our destination is always somewhere fun for him.

But now we have a vacation coming up and will be driving almost 5 hours. Any stops will be determined by my kids bladders. I called the vet who suggested giving him one Dramamine pill.

B almost exclusively sits in the front passenger seat but for this trip, he's going to have to lay on the floor in the backseat. I really don't want to traumatized him or make him regress back into a shaky drooly mess for every trip. Any suggestions for making this easier for him?

I'm wondering if Dramamine will be enough or if I should call the vet back and ask for a sedative. Or maybe Benedryl will be better? I'm not sure anti nausea meds are enough.

The trip isn't for a two months so I can start having him ride on the floor now so he can get used to that.

Thanks in advance for any advice!