I have the lookout full bench for my three and what a blessing it really is. They have their own space, are not crowded together sitting down inside a seat where they can get too hot or uncomfortable. They can stretch out and lay down for naps or just look out the wondow. They each have a toy and a chew and can lay down to chew away.
PetSquared.com - Dog Car Seats > Snoozer Lookout Perch Dog Car Bench