I am not trying to piss on your parade but I have never seen a fan like that used for a Carbon filter setup.
Wondering how much you paid for that fan? What was your budget for the fan or did you have one? Only reason I am asking is due to you telling the shop worker to "hook me up" has me thinking he was trying to off that fan for some reason.
Most of the time I usually see people using Inline fans or Squirrel Cage fans.
If it were me, I would take that fan back. I would go with a inline fan or a Squirrel cage fan (blower fan) the fan you have I do not believe is made to be ran with pressure. It would work great for a intake fan.
If you are stuck with the fan, I would make it air tight as possible to the Carbon Filter. The Silver Metal duct tape works great for this purpose.
Tape the crap out of it so it is air tight. Hang it closest to the top of the tent as you can. Try and run a straight line of ducting if possible. With the Filter being only 17" you could possibly run the filter/fan vertical so the ducting is going straight out the top, or if it is designed to go out the side run it horizontal. My whole point is try and get the ducting straight without any bends.
You probably would get better cooling and filtration if you put the fan at the very end of the ducting so it is just sucking air out and has no restriction of ducting in front to slow it down. This is probably your best way if you choose to use that fan.
Also not sure if you have a Home Depot but you can inline Duct Fan Booster for around $15-20 online and a 6" for $20-35
http://www.google.com/products/cata...ei=jZZMToaQNMfKiAKiyul8&sqi=2&ved=0CFMQ8wIwAA
Anyway I wish you luck and hope it works out for you.