It would be really helpful if you could post some pics, or if you already have, to post a link to them.
That sounds really interesting, using a Rubbermaid or Sterlite container to make an air box; I have several big ones around here.
I'm using rigid insulation that's 1/2" thick:
http://www.homestore.com/homegarden/...store&tran=vud
I have to cut each piece to size, glue it together with a special glue for this stuff, and use silver insulation tape on the edges; I bought all of this stuff, plus the collars, at my friendly AC wholesaler.
I had to make my own boxes over the ducts in the ceiling too, as I use a bigger intake than they normally make insulated duct covers for, and some place on the 'net wanted a fortune to make 'em for me. Actually, that's easier, as I basically just have to cut 4 sides & a top piece, and use a hole cutter to make the holes for the collars, then put it all together.
'Just a question about a fan that big: isn't it noisy, and do you have to feather is down in speed; or possibly you're doing some heavy duty cooling.
Oh, regarding the charcoal filter, it's connected directly to the 6" fan [Elicient] and the exhaust from the fan goes to a room exhaust duct. The larger fan is only for the lights, which worry me the most with all the heat.
Believe me, if I ever did this again though, I'd use reflectors with 8" ducts; you figure the area for 6" & 8", and 8" is actually almost twice as much area.
[3*2x3.14=28.26 sq inches,
4*2x3.14=50.24 sq inches]