timbercruiser, that's a good idea. Using plywood. Hadn't thought of that. I knew if I needed replacements for the present stand, I'd have the daughter use her new hobby of machine sewing and make a zippered cloth bag to hold some foam. Just like the old way. The plywood would provide support on the tree. A couple of year's ago, I bought new foam from a fabric center, for the cushions on the tree stand, and they were like brand new $450 tree stands.
I'll have to look into adequate sized bungee cords to hold the cushion to the tree with the plywood.
Personally, I've been in tree stands, more than four hours, so back comfort became important to me

Speaking of shooting rails. I use one during rifle hunting season, and my original shooting rail had a familiar foam around the metal rail. It was the foam used by plumbers on hot pipes, to insulate them. Intsead the same foam is used to cover the treestand rails and make them soft for arm contact. Since my rail was open at the ends, I merely slipped on a new foam cylinder used to insulate hot pipes. The cost is minimal using these very common pipe covers.