Are you just leaving the cakes whole, and growing straight from the cakes?
If so, birth your cakes on a bed of moistened pearlite. You can do individual tubs of pearlite, or cover the whole terrarium floor with it.
Pearlite is a bit of a pain, but it will provide great humidity at a constant level. I recommend wetting it my running water through it with a strainer/sieve. You don't want the pearlite actually submerged in water, just wet. You may have to re-wet it. A good time to do this is after the first flush.
As for the FAE, I am assuming you are using a tub with wholes cut in the side, with polyfill to filter the air, or you have a ton of small holes. Either way, a fan blowing on your tub from a few feet away should be fine. If your chamber is sealed, a fish tank air pump should work well.
You can even run a fish tank air pump with an air stone (makes tons of bubbles in the water) in a container with pearlite.
The possibilities are endless. I hope some of these ideas are helpful. A good shroom grower is resourceful and creative, so get thinkin!
Be an adult only when necessary.