I took the back cover off during that time that I had dead batteries in my camera, so I have no pictures. Basically, imagine a large rectangular baggie with the opening on one of the long sides. It was pulled over the frame, then attached to the bottom of the frame using wires in listings sewn to the open sides and hog rings - both front and rear. This will become clearer when I sew the new cover together.
The foam on the seat back was in much better condition than the bottom foam. Not surprising, really, when you consider the back gets spilled on, bounced on, and generally abused a lot less than the bottom. The top of the foam wraps over the top of the frame, and if you look closely at the pictures, you'll see that the foam actually has a cord "cast" into it. Holes formed in the foam give you access to that cord, and the foam is hog ringed to the frame. In the case of my seat, it's only hog ringed to the top, leaving the main body of the seat loose. I tried hog ringing the middle of the foam to the frame, and it drew the foam too tightly to the frame for my tastes. I think that if I left it that way, the cover I make from my old seat pattern wouldn't fit. I took the hog rings back off and left it the way I got it from the factory.
I steamed this foam as well, and I'm really happy with the way it turned out. This foam is just fine for reuse as is. The frame is in great condition - no rust or other damage that will make this hard to work with.
Picture 1: The seat back foam and frame. It's not bent, broken, or damaged at all. It is discolored at the top corners because of exposure to heat and sunlight. After steaming, it's still soft and has a lot of life left in it, so I'll use it as is.
Picture 2: You can see how the foam is wrapped over the top of the seat back. The foam looks like it's crushed pretty badly here, but it's very soft and pliable. You can sure see the dents left by the welt - and they're about 1/3rd as deep as they were before steaming. The new cover will crush this flat, eliminating the divot.
Picture 3: These holes expose a cord set into the foam that is used to attach the foam to the frame with hog rings.