I wouldn't stress, seriously. Unless you are over watering or have some crappy (stored outside) soil like I did (I just can't imagine that their was a gnat randomly in my house that found my grow tent and laid eggs) you shouldn't worry. Like you said, you've already procured a few "cautionary measures" to combat this. Also, I'd say get clay pebbles, they aren't expensive and they seem to work wonders for this sort of problem.
I know you said this on my "intro post" about considering switching to Coco. I guess I just didn't read up enough on it. I still don't fully understand why Coco is better than regular (low or no nute) potting soil, just better at allowing roots to grows better/faster I suppose? But yeah, I'll give it a shot for sure. Also I guess I kind of did the same thing as what you are saying, just a different way. I would leaf the dome on for 6 hours, come home for lunch during work, take it off... and put it on the next morning and take it off 6-8 hours later. Also I cut 3 holes into the dome so it would be able to evaporate a little bit.
Regardless, It sounds like baking the medium before is a way to "nuke" it of eggs. Ensuring a fair seedling stage.