Yo, I have a thread on here somewhere that I built a PC case, temps are an issue always, best way is to cycle the air from the top out and have your intake be passive and lower in the case. My case has a fan in the back up top and a fan in the front in the bottom. I originally tried to do something similar to your ducting work with carbon filter. dont bother, get some ona gel or block and that will cover the smell just fine, I just used an ona block to cover the smell of a nearly full box for flowering that measured 2ftX2ft. Now for your light traps get some cardboard or poster board, if you get poster board get black, and if you get cardboard get flat black spray paint as well, the black helps lower the reflectivity of any surface its put on, less reflectivity, less light.
the light trap is a simple design and simple concept as well. I dont have this part on my thread(havent done it for my PC case, just the flower box, but same concept) but itll still work. just imagine your case is 20inches tall, and 10 wide. cut 2-5 15TallX5Wide pices of material and off-set them so that one goes the bottom 15 inches, and the next goes the top 15, the next the bottom 15, and so on... obviously use more material and tape/glue to make a box around the 15 inch pieces, just make sure the one closest to the box is at the top, so you get the hot air out first. if the exhaust fan is at the bottom make the light trap on the inside and have the side closest to the fan be open at the bottom and the other side be open at the top, again to take out hot air first.
for yours dont listen to the numbers i tagged in there, make the measurements fit your grow space. this is just what is going to work for my case and is already working for my flower box.
Hope this helps
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