Wood choice and treatment options

[2sac]

So, I'm going to install a boarding ladder on my Lund similar to this 3 step in the bottom right corner of page 71 https://www.nxtbook.com/dino/LundVol4Issue2/LundVol4Issue2/index.php#/70 I ordered the ladder and need to make a platform. Would I be better off using a high grade plywood or a solid board. If solid, what type of wood? What product(s) will I need to treat the wood before I cover it with carpet? It's already been recommended to use marine grade plywood and gluvit which will set me back over a $100 to make a 16X16 platform and I really don't want to spend that much if I don't have too. Any other suggestions or should I get the gluvit?
Thanks

 

[Ringo Steele]

I would suggest using exterior grade plywood with 3-5 coats of Spar Urethane to seal it up. Be sure to pre-drill any holds slightly oversize and run the spar urethane in through the holes to seal them. It should last a good many years. If you decide on solid wood, white oak is pretty rot-resistant. Teak would be outstanding, but quite expensive.