I stole this idea from a few pictures and places on the web.  I built up small tubes that will house the chain plates to keep water out.  I made them by taking thin cardboard (cereal box), wrapping around the the chain plate.  Then a layer of wax paper, then wax.  On top of that I added 3 layers of fiberglass and used epoxy.  Then cut it to length on a chop saw.  Drilled out the holes bigger (A router would have worked much better....live and learn).  Epoxied them in and was done.  I did install them with the chain plates bolted in, wrapped with wax paper to make sure I didn't epoxy anything in.