Having four players run their own trains is tough on this map. The best training spots I know of are outside of saloon and outside of jail cell. Obviously, the guy with the paralyzer can pretty much train anywhere. Three good camping spots are up on top of the bank next to the couch (Do not buy that couch), the juggernog hallway, and I just did a 56-round solo spending most of the time in the saloon upstairs in the hallway where the zombies can only come in through the door and window.
Things get hairy around round 50 cause it takes like half a clip of PAP'd HAMR to headshot a zombie.