You don't need to spam work benches. Any of these listed structures prevent spawning as well: https://valheim.fandom.com/wiki/Player_base

If you are unsure if it's covered fully go to far corners of the island and bang on crap to make lots of noise. Make sure you are facing away from the island as the game tries to avoid spawning anything in direct sight. If nothing shows up you are good. As long as there is no other land close by (60m) you should also be raid free even though you will get warnings. The possible exception might be fliers as its unclear if the can spawn in over open water or need land like other mobs.