Ok here it is guys. Im going to tell everyone a VERY EASY strategy that works perfect with 3 players. Yes you can do it with 4, but there's a lot more zombies and ammo runs out to fast.

Rounds 1-5: Do the usual start, stay in the main room, shoot the zombies a few times then finish with your knife. I shouldn't have to go into detail here, pretty basic stuff.

If you get a max ammo on round 3-4, stay in starting room another round and stack more points. Leave the lobby whenever everyone is out of ammo or you don't feel comfortable any more.

Ok, now open the door leading to the MPL. Everyone taking turns, open all the doors to the power and turn it on.

At this point, if everyone still has enough money each player can buy the box 1 time, or just buy the AK74u off the wall, it is more than enough power for the next few rounds and is easy to stack points with.

Round 5-10

Now hopefully your team has the power on and one person has enough money to buy the door heading towards the sand trap. Buy this door then head down to the bridge.

DO NOT, i repeat DO NOT open the door at bottom of the bridge. Yes, i know very few zombies come from the cave, but why risk it.

1 person watches the bridge, this person should stand about half way up the bridge.
1 person watches the back window.
1 person watches the right side, I like this person to stand at the bottom of the bridge kinda by the window guy. All his zombies will come in a nice line from the right side.

Play a few rounds like this until all players have enough money for Jugg. This should be done by round 8 easily. Next perk players will want to get is Speed cola. Very important perk for a camping start, since only 1 player will be watching each path, they need to reload very quickly.

Round 9-15

Players should now have at least JUGG/Speed cola and it's time to get guns. After each round or 2 players should hit the box and try to get better weapons.

Here is the final set-up for the haul to 25-30, maybe even farther if your really good and can hold it down. My team can do this until low 30's before ammo starts to run out really fast.

1 guy in back watching the window has the Baby maker and upgraded B. knife/bowie combo for rounds 10-20 is great, he can get ray or upgraded HK/RPK if he wants, but this guy should have the wonder weapon.

The 2 guys that are watching the main paths need to both have Upgraded Hk/RPk's and ray guns. This is mandatory.

Play rounds 10-15 with whatever box guns you get, trying to stack money until all players get the proper guns. After everyone has ray guns, HK's, wonder weapon, your good to go. Make sure your team doesn't run out of ammo mid round, make sure to hit the box in between rounds if your empty. Try to get monkey bombs if you can as they are always helpful.

With upgraded machine guns and speed cola, the 2 players watching the main paths with be fine until at least low 20's before you even need to think about using ray guns.

Guy in the back watching the window can use the baby maker on the bridge when his window is fully repaired and has no zombies to kill.

There will be a point around round 25-30 where ammo will start to run out VERY fast, this is when ray guns should be upgraded to help hold off the horde.

This is a super easy way to get a round 20 very easy, and quickly. Depending on how good your team is this can get you a 30. After 30, to much ammo is wasted every round and you will need to start running loops/trains/circuit around the map if you want to continue and make it to 40.

If you guys need help with this or have any questions ask, right now I have a Round 36, 2 player. I know this strat works very well, we do it every game to make the first 15-20 rounds go buy quickly. Right now I am trying to perfect 2 spots to run trains for 2 player to get round 50+.

Let me know what you think, and if it helped some players up their high round.