R.P.
My daughter does well in the car. She does fall asleep most the time but during long car rides it seems that she only sleeps during nap times if she has toys that stimulate her. Her naps in the car do tend to last a little longer and I do wake her up sometimes. Make sure if there is a certain toys that he enjoys take those in the seat by him and rotate them out or get some new ones that you think he might enjoy to keep him interested. Also I put a mirror up so she could see herself and make faces. Also if need be have you or dad sit by him and keep him up. I hope you have a great vacation!!!