Seats look good !!!
I very much dislike messing with seat covers.
I did learn that there is 4-way stretch material. It is expensive but that's what I use when I have to. A friend sells that kind of material which they make expecially in Seadoo colors. They don't have all the colors but I bought a stash for the skis I'm gonna restore.
I have a few seats to bring to my upholstery guy. He was charging me $150 for 2 seats material included. Probably 200 now.
I hope.