That kind of rail failure is my fear. The long rail is about 900 lbs and required a bobcat to install it. That is why I want to arrest rust damage now.
Your original wood walls lasted 14 years. My "Space Age" wall have been failing for years and now, at year 12, are about to puncture the liner. It is a beaded liner, not an overlap.

If I go ahead with the vinyl plywood walls, I would only screw them in, but I will consider PT 3/4" A-C ply. What did you use between the plywood and the liner?