JP,
It sounds to me that you mean - 'bunks' not bumpers. The long 'planks'
covered with a 'carpet' that support the boat hull.

If that is indeed the case . . . go ahead & use PT 2x4's. This is the stuff
I use to replace rotted or weakened {from rusted bolts, etc.}ones. I've even
made 'auxiliary bunks' from scratch with the stuff. Use all Stainless Steel
hardware & fasteners. A bit more in cost, but they will last practically
forever, and the bunks will last longer as well . . . especially if it is a
'Salt Water boat'.

Regards & Good Luck,
Ron Magen
Backyard Boatshop
{PS - PT comes in 3/4 ply. Heavy as hell and not exactly cheap . . . but
will do the job. Or just use the cheapest EXTERIOR ply you can find. I've
used a full sheet as the 'deck' on my utility trailer for about 5 years . .
.. just looks dirty and no delamination.}

"Jay Pique" wrote in message
ups.com...
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