For this you will need 2-3 players, don't have more than 4 players.

What you want to do is make it to the stage then turn on the power. Use the box and get some good guns.

Now have one player on the stage and the rest in the lobby. Have the people in the lobby just protecting themselves in there and have the other person on the stage doing a zombie train.

To do a train go in a clockwise movement around the stage, shooting at the zombies following you, shoot with the M16 to your right (adapt this to a solo strategy).

Now get to the side so you can see the curtain (go round a few times to gather points and zombies) and go through the doors to the lobby.

Now your friends come into play, when all the zombies funnel in shoot at the center of the stairs where the zombies are coming from, when you get over run go up the stairs and turn on the trap in the room upstairs go back down and the round should have ended...

Do that over and over again.