Baking your soil before use

Any product that uses BTI is really good against fungas gnats.
I am pretty sure those eggs can withstand some pretty harsh conditions.

Bare in mind fungus gnats are predominantly a cause of your soil's environment...

Eggs take only a matter of days to hatch, the infestation more than likely happened after potting.
Also the adults lay where there's rich material and decay. If your roots are being eaten by gnats, there's likely a presence of rot.

I don't personally believe your plants roots are necessarily being eaten by the gnats. And if they are, the gnats are only a symptom of the problem, not the cause.
Don't get me wrong they are a pest, but much more of a nuisance than evil.

More than likely your plants are just a little overwatered. Rich soil, small plants, large pots, easy to do.

I wouldn't sterilize it or else you'll kill all types of microbes including beneficial

You can use pumice stone on top of your soil. Soil drenches with neem oil, and mosquito bits work if you soak them in water first for a day or two. When I did the mosquito bits most of them had fucked off by the next day. The smell must of scared them.

Don’t bother with sticky yellow cards they are only supposed to be used to see how bad your problem is. They aren’t a preventative. You need to make your tent a place bugs don’t wanna be.