ok wait till round 4.(then go up the right staircase) and open up all the doors and circle the whole map. link the tele porter and the main frame. and look around for the box.grab your weapons buy juggernaught then speed cola. then quick revieve. as usal. when you have the linked teleporter camp inside it. when it gets to crowded teleport. throw grenades at the stage and when you run out buy some more and thro some more it will take have the zombies out for that round. when you get back to the main frame run up the right staircase and circle to the stage activate the teleporter when you get back to the begingning activate it then when you get bac to the stage sit in the tele porter and when it keeps geting crowded teleport and throw grenades again at the stage. i just did this technique and got to round 28 but i ran out of ammo. i may have not explanned to good. thank if you try this one day and it helps