If you want to use a Cooltube there are some more things to be observed. It is absolutely obligatory to blow (not draw!) the air through the Cooltube (because the fan and the filter can be damaged if they are exposed to this hot air). This means the Cooltube is to be installed on the opposite side of the filter (because the filter on the other side needs the air to be drawn through).

See picture:

(1) Active Carbon Filter
(2) Flexible Air Tube
(3) Fan
(4) Hose Clamps
(5) Shrink Tape
(6) Cooltube

Here are more photos of the installation of ventilation and Cooltube in a Homebox.