Originally Posted by Docsgsxr
How do you support the middle hinge in the extended position? Am I missing something in the drawing?
Use #23A56CV anti-gravity modules at the front seat edge.
Seriously, you build a normal bench seat but instead of attaching the front plywood to the bench frame you hinge it to the seat and make fold-out legs to support the piece when it's raised to make a bed.
Your carpenter will know what to do.