Create a TeamSlayer gametype called zombies
It must have:
No Shields
No Vehicles on the map at all
No Powerups
Shotgun as primary
Magnum as secondary
Score to Win: Unlimited
Game Time: Up to you (I change it depending on map)
Rounds to Win: Up to you (I have it set to 3)
And the Gametype name must have the word "Zombies" for the zombies logic to work properly.