So my dad wants me to make a couple of replacement bumpers for his boat
trailer. Basically they are pieces of plywood covered in outdoor
carpet. He's insisting that they be made from "marine grade plywood",
in spite of my suspicion that he has no idea what "marine grade" even
means or if the originals were even made therefrom. (from it?)

IAE, I'm tempted to use good old pressure treated ply but for the fact
that I've heard the new stuff corodes metal screws and this gets bolted
to metal. Any thoughts?

Thanks,
JP