Doing the seat backs for the rear seat posed a couple of problems for me - I wanted to cover the aluminum seat back as well as the cushion, but make the cover in a way that it can slip over the whole seat and yet be taut when finished - and be removable for cleaning/repair/replacement. I also wanted to cover the bottom of the cushion but not go up too far, and of course leave room for the hinge pin.
A car seat has room and hardware for listings to pull the cover down into the cushion and give the seat shape, I needed a way to do this too. On this version I put several stitches through the seat cover and cushion, but that ends up making dimples instead of a smooth back, so next I'm going to try either Velcro (but I'm a little concerned with the bulk showing) or cement the cloth portion of the seat to the foam and use the rear cover to provide tension. I'm thinking it might be nice to have a seat back pouch on the seat next to the baggage door for stuff, but that can be added later.
Here's the front view with the cover not completely taut - the Velcro on the back is too thin and just basted in place, which turned out to be almost worthless as a test. Note the dimples...
this shows the back, the not so swift Velcro, and how the cover is put over the whole assembly:
This shows the bottom of the cushion cover (and a couple of unfinished edges):
I will say that making the pattern for this took way less time (I must be getting some of that education) and the actual sewing takes less time than the layout and cutting, unless you get stuck, sew in the wrong order or have to remove a seam.