I started my baby young. She’s been perfectly happy in the car since 4 months old? When I first started, I would always sit beside her, talk and sing to her. I also gave her a musical toy (pull string type). Now, for short journeys, she doesn’t even need anyone beside her. No whining or crying at all.
I know it’s stressful, but keep persevering, and don’t give in by taking him out. It’s for his own safety. Hope he becomes more accepting of it soon:)