Okay I'll chime in again, even though my eyes are closing and I'm HAF. Obviously no one wants gnat larvae throughout their soil. That's #1.
Some of us do no-till, where preventative measures are like
@PadawanWarrior said are used, and they're just natural. He knows what he's talking about. I keep my humus layer that lies underneath my mulch a bit moist at all times. It's not hard to do because of the mulch. It should be a great invitation to pests like fungus gnats, but we build up an environment and population of predators that if any poor little egg laying female gnat fly did come into the tent, it's young would be devoured very quickly. Poor critters, but I hate things with wings that can get stuck in your buds. Lol