This strategy works well. I started using it after seeing a couple of guys do it on youtube. Just search 2 Player Farm Strategy.
If anyone wants to go high runs with this one in solo, its so simple. Like boybad said, stay inside the barn and zombies will never spawn behind you (if you are facing away from the house).
This strategy gives you good opportunity to round all the zombies in one area. I usually train them and then lure the zombies back into the barn and kill them while they just enter. That way the new wave also only spawn around the barn area.
However this method can be time consuming if you do not have the Ray gun.
Many people don't like this map in coop due to the lack of space but I find it quite challenging.
I was referring to camping strategy lol you dont have to train, i have not seen this on video or post but here is the picture showing where you have to stand, there is a window on the right past this door, its not shown here but as long as you dont go past it, they all will come from those doors. You can camp this till 40 but after 30 you will have to hit the box after every round to top up on ammo.