Just don't put him on the floorboard. The floorboard often reaches different temperature extremes and the constant vibration from the road is going to be more stressful. I'd put your ball in a snake bag or a pillowcase, tie it shut and then put it in a plastic bin or a something similiar to keep it from moving around. Also, if he decides to have an accident in the truck, then you won't have a big mess on your seats.