K.A.
Stop the car every couple of hours and take him out of the car seat. Let him stretch and put him down on a blanket so we can roll around. Then change his diaper and put him in his car seat. If you are bottle feeding, you can feed him while you are moving. Fill up with gas whenever you stop and keep snacks in the car, because if he is asleep, you want to keep driving. We drove 17 hours straight (with stops, of course) with a 5 week old, and she was fine.