i actually found this spot a few days ago after learning how to get out of map, heres a tip though.... get juggernog and lay down in the corner and the zombie will stand on top of you and you can get out of the map with juggernog AND mulekick and get the mp40 for the third gun, instead of dieing outside the map.
u can go forever in this glitch! i got to 43 in solo and that was without a trap, just the wunderwaffa, ray gun and HK21. now i can go even farther since u can buy MP40 and the trap!!! infinite ammo basically!