i think you only need a fan for the in hole to the box with the radiator. the out hole just leave it without a fan. cold air will flow out naturally as the in fan will build pressure in the box where the out hole is the only way to release the pressure.
if you place the radiator across the box, it will be better. air will flow through the fins and get cold better. if you place it just on the side, the cooling isnt that good.
__________
| <-in air
| |
|========| <<<radiator
| |
| ->out air
__________
if you get what i mean
