On Ker-Plunk I have two cabin top winches used to hoist the main, jib, and spinnaker. I have installed two Lewmare #14ST winches and three Lewmare rope clutches. All deck hardware uses aluminum backing plates.
When installing all the deck mounted hardware I used West System Epoxy to protect the deck core and fill in the small voids between the headliner and the deck. I started by drilling over sized holes in the deck. The winches are mounted with ¼ inch bolts so I drilled ½ inch holes in the deck. I then had to use some play doh to create a dam to keep the epoxy from running between the headliner and deck. I also used blue masking tape on the deck to protect the deck from any spills or runs of epoxy. Then the bottoms of the holes were covered with blue masking tape (use a lot of tape). I then poured the epoxy in two stages and ended up with a small dome of epoxy above the deck line.
After the epoxy hardened I used a dremel tool to sand down the epoxy level with the deck and re-drilled the holes with the ¼ inch bit. Then I mounted the winch and backing plate using 3M 5200 to prevent water leaking through the bolt holes.