Any tips to get baby to sleep longer in the car ?

I’m anticipating our upcoming holiday travels and wondering if anyone has tips on how to get LO to sleep longer in the car.

A few details...

LO is almost 9 months old. It’s a 4 hour (at least 5 accounting for extra stops for him) trip. We are leaving in the morning. His typical 1st nap of the day is 2 hours, give or take a 1/2 hour. He has never slept more than 30 minutes in the car at one time. I’d really like him to get at least a decent 1st nap in while we drive so he’s not fussy & tired the whole day. I don’t except 2 hours , but even an hour would be great!

Thanks in advance!