This year I took down all my hang ons and replaced all cables with chains using new grade 8 bolts and nuts. reading about falls caused by failed cables got me worried because I leave mine out. I inspected the straps made out of seat belt webbing material. They will fail when the stitching gives up the ghost. The sun and weather will deteriorate the stitching for sure, the belts should last longer.
Have you ever read the manufacturer's warnings? They want you to take them down and store them indoors after every use and replace straps every year or two. Lawsuit protection.
if you replace the belts go for seat belt webbing and polyester (not nylon) stitching. I use Tenex thread, and have an old treadle SINGER leather patcher sewing machine. The Tenex thread is super expensive but basically does not deteriorate, the belt will break from deterioration before the thread.
If you leave your stands out like I do, the cables should be replaced with chains and the straps replaced before the stitching gives out. Maybe add a heavy duty ratchet strap made with polyester thread once in awhile. Think of it as cheap insurance, after all it is way cheaper than a hospital bill!