I havent played for some time now, but didnt light sources also prevent mob spawns inside your base??

Make sure there isnt a dark spot for them to spawn inside and you are good.

ps. you only need the workbench coverage to build stuff, after you have done building you can remove it, you dont need it after.

Edited: ohh mobs cant jump (at least last time i played), so a moat does work wonders combined with well lit areas