I haven't had Bear in the Boxster, but when he rides in the IS, he gets to stay in a $20 nylon
kennel from Target. He loves it, plus it keeps him (and his hair) contained.
You might be able to fit that in the front seat of a Boxster... keeps the dog low and if you were to get in a wreck, more safe than just laying on the seat (the kennel has seatbelt loops).