Airflow in this case goes against common sense, from top to bottom... While at first the idea of pushing air out at the bottom, and thus avoiding the vacuum cleaner effect (ie. all the dust ending up inside the case), seemed exciting, after some thought, it's the recipe for hot pockets.
So I started thinking what could be done to convert it to a more conventional, bottom-to-top, front-to-back airflow... And it's not that hard. You need a fanless PSU, is all! Get one that has ventilation holes on the back as well, which will be the top in this case. Also, flip the huge fan on the bottom of the case to pull air upwards. Add a rear exhaust fan to aid the CPU cooler (which should now be regular front-to-back), there done!