I'd drill and tap a slab of G10 and slap that on top of the deck with 4200 to keep the top layer hole free. I hold my T top on that way. No joke.
Edit:
I know a lot of people have a love-hate relationship with 3M 5200 and 4200. But personally I don't think using epoxy alone in a hole as an insert is a good idea. Historically sandwich core construction uses large diameter metal hard points to distribute a load on the panel. Epoxy without a reinforcement that has a good load path to the laminate sounds like a recipe for a failure. Batteries are dense, so the acceleration loads can be high as you don't have a lot of space to spread out the load. Getting to the underside to insert a bobbin style hard point is impractical, but a elastomer bond to a G10 load spreader is easy to achieve with G10 and 4200 or 5200. The load is only topside, but that is where the thick laminate is, and the load is over perhaps 100 square inches, not 4 or so. And you don't compromise the deck laminate, so the sandwich core can stay dry.
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