Most fans you will find for this application do better sucking or pulling air than they do blowing or pushing. Inlines are the best as they are more efficient, quieter, etc., and also pull air better. This means you will want the fan to be at the very end of the exhaust side, pulling air through a filter, then your cooltube, then ducting (as little as possible), and then to the fan and exhausted.

air flow---->filter--->cooltube-------------------------------------->fan-->exhausted