ive slept in my car a ton of times ... whether it be in the passenger seat or in the hatch. A nice blanket and a couple pillows makes for a good nights sleep.
However the GT seats arent as nice to sleep in as the LX ones ... if that matters to anyone.
I've slept in my Hatchback Stang a few times many years ago. I fit in it pretty good. Just needed a blanket. I pulled over at a rest stop and put some newspaper in the side window and hung a sheet over the seat tops and it was pretty private. For the rear hatch window I put some newspaper together and taped it up. Real cozy.