Cut it off. Cut a piece of conveyor belt to fit and bolt it on. I did it to one of mine that the seat was dry rotted. It's more comfy now than it was before. Next time I'm in the woods, I'll try to remember to take a pic.
But I didn't bolt it to the frame itself, I cut it long, wrapped the ends around the frame and bolted it to itself. You'll need strong hands or a clamp to hold it in place to put bolt through it. It's been about 7 years since I did it. It will never rot. And being black, snow and ice melt off pretty quick.
Go to any gravel yard and they will probably tell you to take all you want from the pile of used belt. I used it for one of my hang-ons as well.