Mode: Vanquish Confirmed (this makes enemies infinite if you don't pick up orbs)
Map: Frontline flats
Difficulty: Easy
Team set up: Zombie Invasion and Plants none
Crazy settings: Ridiculously low health, Infini-ammo and Speed boost craziness
Character: Kernel Corn
You seem to start on opposite sides. In the video I show you how to get to the spot I mention below.
2 minute video by TheOnlyMatto:In the video it may be hard to see so I will try my best to describe. In the map, in the green grassy area there is a cannon. If you stand behind it, you can shoot straight between it and a tree. It happens to line up to an area where the enemy will condense. You won't likely see what you are shooting but you can get roughly 50-60 kills every 2 mins, never raise a flag and I only saw a hand full of easily dispatched foes while doing this. The rest were so far away I never saw them. My shooting method for clearing the area is precise. I am sweeping because they will stop condensing in an area after you shoot there long enough. By moving the aim, they will start to bulk up again.
Alternate route:I use this when I shoot chompers because they have less range and it is easier to set up but it is also possible to do if you kill enough of them fast enough. They won't get near you due to being too busy grabbing their own orbs. This is on the opposite side there is a bridge/treehouse thingy with an overhang. The zombie video spins to show you better