Well, I don't know if this would apply, because I will be comparing your dog to myself (obviously a HUMAN), LOL, but I get carsick VERY easily if #1)I can't see out the windows (I must be facing forward), or #2), lots of stops/starts/turns, etc, rather than driving on a straight road (this applies only if I'm not driving). So what I'm wondering is: Can your dog see out of the windows from his crate? I'm assuming he either can't see out of the windows at all, or he's looking out backwards. I'm just assuming, of course, but if either of these is the case, I would be surprised if that isn't contributing to his carsickness, maybe even the cause of it. I don't know if this is an option for you, but do you think you could try having him sit in the carseat using a car harness? So he can see out and look forward? My pup rides next to me in the front seat w/a dog harness on, so he's safe and can't move around (luckily he just sits in his seat and doesn't act stupid in the car).

I would try this before anything else. I know we can't always compare dogs and humans, but sometimes things affect us the same way, whether we realize it or not.

If you try this, please post and let us know if it works. Now I'm curious. Good luck!

Kori is right... I used to be a SCUBA instructor and had to deal with motion sickness all the time. Your body(and I'm assuming a dog's) can adjust to a predisposition to motion sickness, and the best way is to be able to look at something on the horizon (or in this case, looking out of the front of the car).
That being said, it may be quite difficult to accomplish this with a dog in a dog crate.
Ginger and other herbal remedies are great to settle the stomach, but don't do much as far as combating the motion sickness itself...

We have 2 vehicles (Toyota Highlander and a Chevy Crew Cab truck).

She is usually in the back of the Highlander with the seats folded down or in the back of the truck with the seats folded down. I roll down the back windows about 1/2 way so she can sniff outside. She is free to look out the window or lay down.

She is ok on short trips, but got sick within 20 minutes the other day on a longer trip.

I'm still hoping that she outgrows it at some point. I just put down and pack lots of towels when I take her anywhere.