Because it gets cold here in the winter, Cali has a car seat that can be heated when needed - she loves it and gets really cozy. It has a teather for security, and she can see out the winter.
Amazon.com: Heated Dog Booster Seat Medium...
If you put them in the front seat be careful of the airbags. My car has a way to turn the passenger air bag off when she is in the front seat, but it could be dangerous if it deployed.