I've put off doing this project in hopes that someone else would first, lol! Looking at the wood pieces...approximately how thick are they? Obviously custom routed/fit to match the profile of the sundeck. You say you are thinking of using a "plastic based wood product" for replacement? What sort of product? Would something like this work:
https://www.lowes.com/pd/Royal-Build...Board/50092326

Personally I would use King Starboard for replacing the wood around the hatch. In my Active Thunder there is no wood used anywhere and the bolster seats, combing panels, engine hatch cover all are King Starboard underneath the upholstery.
https://www.boatoutfitters.com/mater...king-starboard

I like the Starboard idea, then drill and glass the t-nuts in place.
if you don’t want to fight taking all the staples out of the hidem strip you can order new from Albrights in Corinth Miss.

The old wood strips are 1/2 inch thick. The PVC board you linked would work but needs cut down in thickness to 1/2 inch. Starboard would work too. Just use the old wood for a template and transfer the shapes onto the new product and cut out with a bandsaw or jigsaw. Router the outside edge to get rid of the sharp corner and the holes for T nuts can be located by the existing holes in the fiberglass bottom of the sunpad.

I see your boat has Sunrise Beach as the home port. If you live close to there I would swing by Waves and Wheels to ask Noah if they have a few strips of starboard in the length you need. I would bet they have some scrap pieces in the length you need, since they use it quite often on projects. It would be way cheaper than buying a full sheet.

Thanks. I will do that. Jim

The hinges attach to the sunpad by going thru the fiberglass and new plastic strip. The strips are held by T nuts and bolts.....all rusted together in my case and replaced with stainless. I did not remove all the vinyl but just pulled it back enough to expose the area I needed to work on. I could donthe same job next time in about 2 hours if all materials were ready to install.

Awesome! I am glad to see the final results. I'll be doing this job myself come Fall, more than likely.