i have severe thoughts that would help anything, take a look at Unicorn Reviews video on fan stacking, he does it for cpu cooling, but i figure it is a similar concept. realistically i think one fan would bottleneck the other or one would just push more than the other. so i dont think it would be 2x the performance.
Just stacking them on each other will do nothing or less in some cases. What you want to make is an asynchronous turbine and that requires baffles to be placed between the fans to straighten air stream before hitting second fan as well as higher airflow rate of second (or subsequent fans. That's why push-pull fans works on coolers for instance.