Rashiik and me made a 40x40x6 storage room with chests on the walls and lights that could be turned on and off (to avoid our base being found through shadow glitches)
It turned that mobs started spawning when the lights were off, including zombie villagers. Now we have more than 30 villagers on our base. I think this is the most efficient method if you live underground. I wouldn't risk opening any tunnels to the surface...