I haven't had any problem with it and I think some evaporation creates a better environment with more access to oxygen and better aeration versus fungus/mold. When the surface soil is nearly dry (patchy mostly dry) or just becomes completely dry is when I give them a spray to dampen them again (there should still be some humidity rising up from below them). If they're not too close to the lights this is maybe daily, perhaps a little less often. If it were drying out too fast on me, I'd probably leave the bag on during the light cycle and remove when they're off or something like that. Personally, I don't feel it's all that delicate. As long as they're not overly wet with bags on all the time you're probably good.
How's it going? Are they starting to sprout for you yet? You're what, just over a week in now? For the varieties on your list you should be starting to see some hooks, if not already, soon.
