The back of the Tesla is very large. I’m 6’3″ and I can stretch out lying down with the back seats down, no problem. However, it’s uneven. There’s a 2 inch ‘hump’ between the cargo area and the backs of the seats when they’re down. So, I’ve built it up with a few layers of cardboard covered with felt. Combined with a nice thick therma rest, it makes a nice comfortable place to sleep.
I know the finished product still looks a bit uneven, but if it is, it’s only barely so. Definitely a huge improvement over having a 2 inch bump right where my hip would be.