A reader wrote into Practical Sailor that his LifeSling had basically fallen apart, the result of UV exposure. The blue webbing straps tore under hand pressure (a write up in PS will certainly be forthcoming). The age was uncertain (probably more than 20 years) and I believe it may have been stored upside down, since the straps should be on the bottom, completely protected from UV.
But the other issue is that the LifeSling cases are notoriously UV sensitive, or rather parts of them are. I bet the failed LifeSling was in a failed cover. The coated polyester itself is pretty durable, but the stitching goes and all of the Velcro fastenings go at about year 5-10, depending on the latitude and whether it sits on the rail year-round, like mine does.
Packing. Packed according to the instructions, all of the critical parts are well protected. The line (VERY vulnerable is in a tube in the center, with the sling over it; triple protection. After 19 years, mine is still pritine. The tail of the rope that attached to the stanchion base is covered with webbing. Although the webbing is sunburned, the rope is fine.
I cut a section open to look. Note that there are a few failed strands on the lower left, where sun must have peaked in. Polypropylene is touchy stuff.
Velcro Top Closure. I dislike the UV vulnerability of Velcro, so I replaced it with a tubular webbing and pin system, something like a door hinge. Just pull the red flag. This endured for 10 years without damage, so I left it alone this time. Durable, secure, and fast.
Velcro Ties. Really, a stupid application, when a knot will do better and last forever. Again, the Velcro fails in 5-10 years, I cut the remaining stitches, attached a 2" x 4" webbing strip on the inside with Sikaflex, a 4" circle of Sunbrella on the outside with Sikaflex, and punched a pair of holes. I was going to install grometts, but the laminate was too thick, about 1/8", so I simply threaded webbing.
Stitiching. Some of the seams had gone at 10 years, where they rubbed on the rail. I hemstitched them 10 years ago using whipping twine, and they are still fine.
Paint. I had some white vinyl inflatable paint left over, so after a good TSP scrubbing I painted the whole thing to provide some sunscreen (I masted off the instructions--that section seemed OK and has no seams or stress points). I have used Kilz primer plus house paint on projects like this before, through, so don't run out and by special paint.
I will 20 minutes work I should get another 10 years from the cover. Since the initial cover needed repairs at 10 years, I'm OK with that.