Welcome, Sofadoc!
I like your approach to this. I see a lot of new sofas that are made this way -- the back, the deck, and both arms are made and upholstered separately, then screwed or bolted together.
At least the bed won't fold out when it's halfway down the steps and trying to turn the landing.
I have been a frequent user of other discussion boards, this is my first visit to this one. I hope to enjoy this one as much as the others.