Lol i did this with couple of friends..The fcked up thing is that when u go together and 1 go out the glitch is pretty anoying to quickly buy ammo and go immediatly back in the glitch, if ure little to slow zombies will come and get u..(zombies that still spawn outside)
We also did that 1 stayed in the light house down but that kinda sucks aswell because the person outside cant get out of the glitch because otherwise ure teammate whill die.
I think the best way is (with 2 people) to stay both outside and when u want to buy ammo wait for all the zombies to be inside, because they will keep following the one thats still in the glitch

..
But if u go out the glitch and some zombies spawn next to u, u cant make an fault like i did today where i quickly went buying ammo and quickly run back into the glitch but i wassnt right..
i kept moving because i was close and needed to hurry ^^ And then i went into tilt

i was in the glitch but for some reason i jumped off because some zombies was about to hit me (i tought) and later i died..
So dont go out of the glitch when theirs zombies outside and u cant do it fast enough xD