The materials I am seeing is vinyl, real leather is very hard to get where it's thin enough and is difficult to get to follow tight contours, this requires a lot of work, vinyl stretches very well, I use super glue fix all, I have never had it bleed through, and it doesn't make the material hard or brittle, white glue is also a good glue for almost all materials, but I think the problem that would occur would be it wouldn't want to bond well enough to plastic to hold the stretching. Just a side note, these car seats are absolutely amazing.
When I started modeling I found a book that was written by a master ship builder, it is a very good book, after looking at all the pictures and returning it to the shelf for many years I stumbled upon it again, I normally build wood models, I read it, this man had a section that really took me aside, the section was on clamping, this can be a very frustrating issue when assembling, well almost everything, with the plastic I found myself re inventing everything I've learned about clamping, looking now at your tools, well it seems you've mastered this as well.
Thank you, for the kind words. The decals came from Google images. I did see the kfs binders, I was concerned with the time line, I am very satisfied with the moluminum binders, I certainly had no intentions of putting them down, they are very nice, I don't spend enough time building model cars and trucks, I hope to change that.