You get your humidity from your medium. Whether you use vermiculite, perilite, hatch rite, cypress, it all works as long as its done right. Putting water in your incubator in either 2liter bottles or whatever acts as a thermal batterie to keep temps stabilized. For example, i have a walk in incubator. I basically built a walk in closet that is 6 ft wide by 5ft deep by 7ft high. I have a glass door so i can see in my incubator. I also have a number of 5 gallon buckets filled with water with tops on them that act as the thermal batteries this keeps my temp swing down and stabilizes the temps. I used to have open containers with the mindset of it will help with humidity. It doesnt really matter. The humidity is created in your egg box by your medium. I use a space heater as my heat source and a non porportional thermostat. The reason i dont use a proportional stat is cause there isnt any on the market that can handle wattages over 700 without blowin fuses yet. But i am high on the list with jeff at helix for the new dbs 1500 watt helix that should be out in a couple weeks so i will be switching to that soon. Also air flow is important. I have my fan high pointing down against the heat source so it basically plays ping pong in the incubator. I can now keep my temps stable at 89 degrees after a little fine tuning with jeff at helix. Oh by the way he is the man. Anyways i know this has been a long winded response but in short your medium promotes humidity