Some dogs travel easily and some don’t, it’s as simple as that. One solution to the problem is to not let the dog have food before a journey.
While this means it will have little or nothing to vomit back, it’s extremely important to ensure the dog is watered regularly on a long trip and to ensure you stop regularly en-route for him to stretch his legs and get some fresh air.
Have some sympathy with your dog because you know yourself how rotten you can feel when confined in a small, cramped, airless car especially during hot weather.
In fact a dog box in summer can get very hot so ensure there is plenty of ventilation circulating through the vehicle to keep him cool.
Keep the journey as stress free as possible with no loud music, shouting, and no treats.
If, in spite of your best efforts, the dog continues to suffer then ask your vet for advice on useful sedatives or suitable anti-sickness remedies to administer on long journeys.