Re: Partially filling a void
Aha.... the 'bottom' layer is the liner, then? Are you sure the deck side is not cored? If they've bolted through the deck and the liner to that's unfortunate.. as you say the parts compress.. usually the liner ends up cracking at some point, they are usually pretty thin.
If the deck is cored there (likely) I'd be very tempted to drill some nice clean 1" holes in the liner below at each throughbolt, rebolt the traveler with fender washers (to the deck proper), and then find some bungs (you can get plastic knockout plugs from an electrical supplier) to close the holes.. it won't look as clean, perhaps, but your traveler will thank you...
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)