Doubtful if the ECU gets enough cooling this way, but then again, they were supposed to operate good in an engine bay aswell.

I personally would like to create some 'forced' cooling with either an extra little fan blowing at it, or put it in a place where it gets fresh air, like the front of the radiator support.

I've ran a Mopar gold ECU once which lasted exactly 1 run. On the far end of the track the engine barely kept running and was just able to make it back to the pits.
It was however mounted high on the front of the rad. support frame.