https://www.kingplastic.com/products/king-starboard/
Starboard is probably what I’m going to use at least for the sliding portion. I’ll use a 3/8” thick piece in place of that plywood.
We use it on boats a lot to build cabinets etc because it does not rot. It also makes a good sliding surface when needed.
If trying to save some $, follow boywonder’s comment above about the plastic cutting boards. Find a used one and cut to size. Tell your significant other when you’re camping!