B.W.
He'll be fine! Just remember to take stops every couple hours, time stops around his nursing times and mealtimes, let him play a little and get out of the carseat. Since he's still rear facing, you and your husband could take turns sitting in the back with him while he's awake and the other drives to keep him entertained.
Bring small snacks like Cheerio's, crackers, small toys and don't forget his favorite blankie or stuffed animal/lovey.