Rubbermaid + Vortex + Carbon Scrubber = confused

Ok, so ive got these three things. a rubbermaid growbox setup, a 8" vortex fan, and a carbon scrubber. now ive got to put them all together, the question is how. i know ur supposed to have the fan pulling air out of the box and then push it through the scrubber but could someone clarify a way to do this. ive got some 4" flexible ducting leading off the scrubber and im baffled as to how to affix it to the fan. i took the base off of the fan and mounted it on the box but the resulting hole is so huge that its gonna leak light like a summbitch during the flowering cycle. im probly gonna have to rebuild the top half off the box with a smaller fan hole but then how do i get the fan to fit and suck air out. Any and all help/comments/criticisms welcome.