How many days will I be able to stay inside the shell lying down?

I have been trying to figure out how to have some headroom in a camper shell. Trying to figure out what I would need headroom for.
Then I saw this from The  Rockler site:
A folding bed.
That would give me some sitting room, sitting on the floor.  Could it work? Maybe.
I am looking for a way to have 36″ of headroom somewhere. Whatever the height of the shell is, that is the headroom. I would love to have a fiberglass, low shell, not the commercial aluminum one. However the tallest non-commercial shell is 25″. There is a commercial one that is a wedge, going from 30″-36″. Tempting. Possible.

How about a hammock hanging from the ceiling? How about a take on a Murphy bed?

How about a pop top  shell?

Any ideas?