Hello all!
Happy Holidays!

I am in the process of constructing a highland terrarium and would like some advice. The terrarium is ~ 122cm long x 61cm deep x 56cm high and I need to address the issue of humidity. In the event that my method of cooling (2 fans circulating air through a closed system containing the terrarium and a small dorm fridge) should force me to use a humidifier, which type should I choose?

(Click to enlarge)
My parts list has changed quite a bit since I originally did this so let's just ignore that.
The purple dots on the side of the box indicate openings where duct work will attach and connect to the comp fans on the sides of the cooling box (the dorm fridge).

I have read past posts regarding terrarium construction in which people have used the "submersible" cool mist ultrasonic humidifiers commonly used with reptile enclosures. I have also read that they can suddenly fail or that the internal membranes are near impossible to find when in need of replacement. Is this true? Also, if the consensus is that I use this type of humidifier, would it be better to place the humidifier in the cooling box or the terrarium itself?

The "home remedy" type of cool mist humidifiers seem to be the more commonly used with the more experienced growers but are also slightly more expensive. Also the addition of ducting to transport the mist is something that needs to be addressed. I suppose it wouldn't be too hard to rig up one more piece of duct that would connect to the cooling fan tunnels should I decide to go with this particular type.

Thanks a lot for your advice!