Assuming rust doesn't get the frame first, then the thing that kills things like these is UV in sunlight weakening the fabric and stitching of the seat. With the single piece seat, once it starts to go, the damage rapidly runs across the entire seat. With the separate straps, one can go without taking out the others, but they are all of a similar age, so won't be far behind. Storage inside when not in use is the best way to a long happy existence for the seat.
Not a lot in it really!