Are you wanting to give this to him for all short trip or one long trip?
Thank you for that information,
while you can give a dog dramamine it is not without side effects and should not be used for frequent short trips. I will direct you to a site that goes over side effects and dosing. http://www.petplace.com/drug-library/dimenhydrinate-dramamine/page1.aspx
You may also want to talk to your vet about using the drug ACE . You can read about it here. http://www.petplace.com/drug-library/acepromazine-promace-aceproject/page1.aspx
It may help for you to get her better used to the car by doing it in small increments.