Sappers will 80% of time evade go through that entrance passage because of the turrets, not Breachers thought (these will not attack the beds, only if they spawn all the way down the map), The 20% of attacks happen on that left top corner with the beds ( that has less layers), but if you have more layers on around like the rest of the base, sappers should 100% evade attacking the beds, and only going trough the entrance of the base, there you can blast them all.
One last thing to add, you can add fences with the turrents around the base so that insects can only spawn on the fungus plantation in the dark.
About that single turret at the entrance, it's so they create collision and don't stack up, they will do this "pathing" where they will enter one at a time. kinda need to properly fix it because it sometimes doesn't works lol.
also the kills box, i never set it on fire, but i noticed i didn't add a door to keep the heat from spreading inside the kill box. lol
just add one there would ya? :D