You use 6 Siege Tanks on teh main two paths, and two tanks on the third path, backed up by perdition turrets. Upgrading weapons for tanks makes them kill even more in one shot.
This Strategy... Lasts you for forever as the Tanks usually kill everything that comes into sight, if your turrets never get damaged, then you can go on forever.
I honestly feel that Outbreak on Brutal Difficulty atleast, needs to be De-nerfed.
Tanking with firebats in the beginning works very well, just put them on hold position, put medics behind them, and concentrate on getting the tanks and turrets made. You're golden after that. It is Brutal Difficulty, Outbreak is the only mission i can do on Brutal, except for the first mission.
My ultimate point is, Brutal on Outbreak isn't really proportional to, say... Zero Hour on Brutal Difficulty, in fact it's easier than Zero Hour to be honest.