You might want to check out a product boaters use. I believe it's called "Wonder Board". You can cut it, drill it, do anything with it that you can do with wood. But.... it will never rot, because it is made of what looks like plastic (white). It comes in 4' X 8' sheets. However, it is not cheap. the last time I checked, it was just over $200 a sheet. But you can buy smaller sheets than 4' X 8'. It works great!
Roland & Jerri, with Maggie & Mollie, our Pups; '05 Fleetwood Providence, 39' DP; '08 Saturn. "The difference between genius and stupidity is genius has it's limits" (Einstein)