Workbench/fire/torch/etc "spam" doesn't technically stop raids, but it does stop the monsters from those raids from spawning. If you're on an island, the bat raid can still happen, as flying creatures can apparently spawn over the water. I'm not sure about Gjalls, as my main base isn't in the ML. Only have small portal outposts there, usually in mine towers, previously owned Dvergr towers, or ruined towers.

But having an enclosed base on an island with no monster spawns that can only ever be invaded by bats is pretty sweet.