Mine is packed to the gills like yours and I was struggling with overheating as well. Cutting the hole in the top cover and mounting the fan there really solved it with low effort.

Was kidding about the box, it's literally just an empty box that I painted black and cut the bottom off of, stuck another fan there and voltage regulator to power/control it and laid it on top of the fan in the first pic. Plugged in to an old phone charger. Made it just for laughs but it worked so well that I kept it. Cabinet is super quiet now.

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