There are many materials out there but you need to understand their capabilities in your application, cost is another consideration. My boat builder used starboard in place of wood in many of the seating and cabinetry components.

Treated wood that you find at Home Depot is "heavy", there is a marine treated that is dry! I just used it to redo my hatch head rests. It's the stuff that they originally used in our boats. I figure mine lasted 17 years, so it would last long enough. I also applied more fiberglass in those areas that were rotted to divert water away.

I know what you mean, but a lot of the failures are not directly related to the fact that they used wood, rather, it is poor construction techniques or cost cutting, "don't give a damn" measures that lead to water intrusion and rot. Running screws straight into the core without properly sealing it, cutting holes without lining the hole with resin and mat, etc. The best way to put a screw into an area that has a wood core is to first drill the hole oversized, then fill it in with epoxy, and then drill to the proper size and run the screw in. But very few boat builders will take the time to do it that way. You are lucky if the guy squirts a dab of caulk on it before he runs it in crooked.

I've used P/T'ed for seat backs and such. I've even used it for stringers in my Biesemeyer. Just have to buy it and let it "dry out" for a couple weeks before working with it.