Cool design!!!.
Just to improve on your idea slightly I would suggest that each joint be sealed with something like [say] silicone gel prior to screwing. Not all wood is flat nor can be cut 100% evenly so.... just to block the gaps. You wouldn't want, for example, to be sucking smelly air into the "fan chamber" through the joint along the fan chamber and expelling this unfiltered air. Sounds like your's was soundly constructed though, no gaps anywhere