This is one of those "well, I did this other thing" posts.
I decided on 1/4" HDPE plastic for a keel strip, because its cheap and I knew I would cringe over grinding away a metal strip on ramp pavement or whatever. I used G-flex epoxy and flame-treated the plastic to help the epoxy stick. I figured the plastic would be a little slipperier for launching and retrieving off the trailer, but I don't know whether that's actually the case. Three seasons- so far so good.
Bob