I have seats and seat backs on ladder stands that have rotted. They are "sling" style with no metal supports. The manufacturer won't sell replacements because of liability concerns. Have you had a good experience with any of the generic replacement seats on the market, or can you suggest a DYI solution that I am not thinking of?

I have made a couple of seats out of spare safety harnesses that come with stands. Used the tree straps and longer pieces to weave a new seat. Sew it together with upholstery thread and a heavy needle.

I used gorilla tape years ago to replace a seat and it still is fine. #redneck

I saved the safety netting from an old trampoline. Cut out enough so I could fold it and make it 4 layers thick. Took nylon bailing twine and sewed it to the stand. Comfortable and has been in use for 3 years.

stair treads and swing set seats come to mind