Think there was a thread here about this before. Search a little and you will find it. I have posted this image in that thread:
I was alone in the car and had even space for my bike beside me inside the car
I have heard of and seen images of a couple sleeping in the rear of the car.
Just push the front seats a little forward and the rear seats down.
You can ofcourse sleep in the front seat, but that is not that comfy.