The cool tube will likely be 6" diameter so I'd stick with ducting, inline, and carbon filter (you won't need a huge one for just 54 cubic feet) that's 6". You won't need to run a 6" inline anywhere near full speed with just a 400w so buy any decent brand and with the money you save from buying an expensive 'silent-y' inline, buy some insulated ducting, a fan speed controller, and a duct muffler.