As long as there is no moving air around the radiators, they won't cool much. Even your case with all rad spots filled will likely not be enough to cool your system long-term. It might work for short loads, but after a few hours it will get warmer and warmer. Just get nice and quiet fans like Noctua NF-F12 and run them at 500 RPM where they are not audible. Then you can just use 1 or 2 rads and the temps will be fine.