Good Four Player Strategy for Nazi Zombies Der Reise

In the beginning pick a window and just let zombies come through the barriers for the first two rounds and knife them, this will cause you to get Max Ammos, Double Points, etc.. Level 3 and 4 Use your pistol and knife, unload a clip into each zombie and then knife them still letting them through the barrier.

Level 5 open up the door near the Gewehr 43 and buy the carbine and then open up the doors to the mystery box.  Use it once or twice but dont use the weapon unless its against dogs. Use the carbine aiming for head shots until around round 10 or so, i keep it sometimes the whole game.

After round 9 open up the door that leads to the very back with the teleporter.  Have 2 people cover the stairs, and 1 on the window at the top of the stairs, the 4th can vary from helping the 2 on the stairs or shooting out of the windows at the zombies coming.  Try to make a crab ( a zombie that has it legs blown off) and link all the teleporters and use the mystery box, get perks, upgrade your guns, and repair the barriers. Do this every round to make sure your team has a good ammo supply.

By level 19 or 20 you should have both guns upgraded I recomend the PPSH and the Ray gun, Ray Gun and the Wonderwaffe. Just try to get the ray gun, use it until the ammo runs out then go upgrade it. By level 25 your whole team should have ray guns and at least two should have monkey bombs use these when team mates are down.  But you should probably start to move around through the map using the traps and the teleporters

Ive used this strategy to round 34, so you should have some sucess with it.