So life happened and I got pulled away from the project for a while. I've been able to get some work done on the seats and am happy to report that 1 seat is skinned. I mounted it with some off the shelf Menards rivets that I found. The are aluminum and painted white. The stud 90% of the top pops off flush are just below the head and stays retained so I like that. I debated using some kind of adhesive with the rivets and decided chances are I will be re-doing this and didn't want to have to scrape a bunch of gunk off. I may regret that due to vibrations and flexing, but I will keep that up to date.
I started withe the bottom. When I skinned this I didn't have Cleco's (I've remedied that) so I drilled the panel out, attached a few rivets. Drilled the rest of my holes, drilled out the rivets and cleaned off the burrs and re-installed.
I installed the back and then had to move away from the sheets that sat on the square tube and move to the ones with round tubes. I chose to just go about half way around the tube and then drill a hole riveting thorough the round tube. It would have been better to add a flange to the round tube and just rivet flat to that, and I might do that If I do this again, but these seats are an experiment and I thought I'd try this. I formed the metal around and relieved it by cutting out metal that needed to shrink and fold over. It doesn't look the best, but it is functional. I put generous radius's and cut back quite a bit from all of the edges to try to minimize any tearing that may occur in the metal. Again visually it's not the best, but it will be covered in fabric eventually.
So the drivers seat is now skinned. Next steps will be to upholster it. Sitting it is is surprisingly comfortable even without foam. I've used it sitting in the living room for about an hour at a time and was comfortable. When I foam it I will add a lumbar support.
It's obviously a lot of work to build a seat this way and I'm not 100% sure that it will survive, however the real cost to date is ~$20, so other than Time I'm not out a lot if I have to re-do it.