Re: Replacing decking with aluminum
I just happened to be up under the deck of my alum bass boat recently. The hull and deck are made from .100" 5052 grade aluminum sheet which is high grade of alum; very strong for it's thickness. However, the boat has a lot of aluminum framing braces behind it to support it. Mine isn't noisy as it is covered in OEM outdoor carpet.
Alum is lite. On wood, I'd use marine grade plywood which will give you high strength and minimum thickness. Marine ply uses marine waterproof glue and multiple layers as compared to the same thickness of cabinet grade or worse wood and that is where it gets it's strength. It is wood however, and wood can rot under the right conditions. How long that takes depends.
Agree on covering it with glass mat which adds that much more weight if you are into the long haul. If not, a good penetrant like Boiled Linseed Oil and turpentine 50-50 works well then covering with heavy duty vinyl. Rumor has it that the store bought wood sealers don't contain all that much Linseed and that is what keeps the water out of the wood. Only problem I would have with epoxy would be it cracking and letting water in. As long as it doesn't crack, fine.
My 2c,
Mark