Does he have a "den" within the truck? A covered bed, or crate? That might help.
My Bentley will lay on the bunk, while the truck is stopped, but as soon as it moves he gets under the bunk, in his bed.
He Loooovvvvves, truck rides! He doesn't go very often though, cuz I don't let him away from my site, and I don't like to go!
