Heres how I did this on solo:
Round 1: Allow all zombies to break through and then knife them since it is one-hit kill. Leave one zombie alive so that you can repair all windows.
Round 2: Allow some, but not all zombies in as it is no longer one hit kill for the knife. Unload a clip from your pistol into zombies then stab. If you don't get Max Ammo and run out, throw a grenade at packs and then stab the survivors. For one or two zombies, lunge in and stab, then back away wait to heal and repeat until they are dead.
Round 3: Open up the left door (if you are facing away from Pack-a-Punch) and get to the power switch and random box. Open the random box and buy a gun, then turn on the power and wait for the zombies in the area behind the power switch. If you have the money and an opening, open up the random box. Best guns are Wunder Waffle, Ray Gun, Browning, DG42 or Ppsh. They kill dogs and zombies well. If you don't get any of them, you'll probably die, but try for automatic weapons then.
Rounds 4 onwards: Continue to fend off zombies and purchase weapons from the box. If you see a large group coming, cook a grenade and throw it at them. When dogs come, pick a corner and fend them off. When the box moves, try to make a crawler with a grenade or a molotov if you got one. With the crawler, try to open as few doors possible to reach the box. If you open a room with a teleporter, you may as well link it to the mainframe. (If you have to open the building behind you, camp either on the cat walk in front of the box, or at the end of the underground passageway.) When you run out of money, repair all windows, kill the crawler, and fend off another wave. Continue this strategy until you get the achievement or die.
NOTE: As we are all well aware of, this achievement is entirely luck-based. You may need to open the random box 3 times, or 300 times. I am simply giving you the method I used to get it. Please rate and comment.