I'll bump your thread again...hopefully someone can respond to answer your question.
I have a different rig, and obviously a different type sofa, but from what I've seen when taking the storage drawer out from under ours, the sofa is a very basic piece that's just screwed to the floor of the slide...
and I understand from reading other posts in the past, that the arms detach easily to get it in and out of the coach.
Send me a message if you decide to move forward with the project. I'd have to check with DW but I might...maybe... be interested in your sofa if you decide to get rid of it.
It looks like it probably sets up into a bed much easier than our air mattress. We'd loose our storage drawer that's under ours, and unfortunately it looks like it has the same vinyl that failed on ours...but it still might be a solution for me if it fits.