I noticed the seat above the furnace seemed loose. When I raised the cushion, I saw that one of the structural supports had come free from the staples:
Drilled, countersunk, and screws:
To answer an earlier, but now irrelevant question I had before, it would be quite easy to move the furnace if you wanted to convert a sofa model into a dinette model. The most technical parts would be rerouting the gas and electrical lines.