My dog is a bit bigger (62 pounds) and in a pinch when I have to take him somewhere in my car he has to ride in the front seat.

The back seats fold down but it wouldn't be a comfortable ride for him, plus I don't know how well they'll hold up with all of that weight moving around a bunch like dogs usually do.

 

He's usually restless for say half an hour, then just goes to sleep on his little bed we bring along with us.

 

The rear seat backs can be removed easily in about 10 minutes. The seat bottoms pull out as well. This should provide ample space for your dog.

 

This summer me, my girlfriend and our 3 year old daugther made a 600 Km trip (one way) and we were out for about 5 days in my 996 C2 2002. My daugther has a backward facing baby seat and I have removed the rear back rests for more leg room for her. On the way home we actually stopped at a discount store and bought a lot of clothes, blankets etc (about a normal shopping trolley full of cloths). IT WAS TIGHT BUT NO PROBLEM! As long as you use soft bags, the frunk swallows quite a lot of stuff.

Robert