Since there is a return (lip) all the way around the perimeter of the seat, you could also glue felt on the back of the seat. Its very flexible and installs easily with spray contact cement. Just spray the seat and felt, allow to set and carefully stretch on the the seat back. Trim to fit. It would be simple and inexpensive. Finished product would look very good. Its the same type of felt used inside car trunks on customs.
I used felt on my seats but because I did not have a lip, I sewed a binding edge around the perimeter.
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