Moon is a really tough map, its awesome! i played a few times with a friend last night and we found maybe 1 good area to hold that was sucessful until the late teen rounds, running a circuit seems to work but its easier to co ordinate 1 place to lockdown if you have the firepower. aside the place im about to describe have any other places worked for anyone?
When you reach the room that has 1 door going outside (where mule kick is) and 1 door going into that dome thing with the jump pads go outside and round passed the teleporter onto the walkway. there is a door that costs 1000 that you should be standing next to that leads into the dome. do not open it. this is a decent place to hold and in the early rounds you can even do it with the ak74 that is nearby.
the zombies spawn on only 1 side of the walk way and they climb over the railings, you need 1 person holding them off here and its easy because they come up 1 at a time and their heads are always in the same place. save the ammo and go for the headshots. the other person needs to hold them off from coming round the teleporter. even when there is a lot of them coming some seem to fall down where the teleporter is so that thins down the train of zombies and stops them grouping up and becoming overwhelming. needless to say whoever is doing this should have an LMG.
there is some problems with the place, if you do get cornered and have to use the door into the dome you are screwed for next round, if you do use the teleporter and it hasnt cooled down till the next round no zombies fall down the hole and also if the spaceman comes you cant run. finally, the person killing the zombies at the railings is doing so before they zombies enter the map so there are rarely powerups, letting them in to such a tight space is a big risk.