water down the mast
I would drill a small hole in your mast so that the wires can emerge 6" to a foot above the deck. Then I would pass them through the deck through a wire thimble through the deck to a connection block below the deck. Then seal the hole below the deck. Option 2 is to install a wire thimble in your mast step. Wire thimbles are metal fittings with a rubber gland that seals against the wire.I usually use a little silicone around the wire at the thimble gland.