I'm 6' and have the front runner interior rack in mine. I've moved the gear onto the interior rack, folded the middle row flat, stuffed a towel in the crack, and slid the front passenger seat forward. With a 3" thick sleeping bad I slept way better than I would have in the crazy wind outside. But as others have said, the folded seat is at a slight angle. It's not uncomfortable since you're entire torso is on that angled part.
Now I'm considering adding a short drawer system that would let me create a flat platform with the folded seat. Being able to sleep in the Jeep is awesome when you're solo. Especially in foul weather and on fast paced expeditions where you roll into camp late and break down camp early each day.