Will runners from round 2 be enough?I think you might make some people mad if you do that, haha. Just add a blocker at the beginning of the tunnel. Then add risers and a new zone for them behind the blocker for just the tunnel. Then at the end of the tunnel put a third blocker. Attach the spawners in that small area to that third blocker.
The key here is to separate these huge areas - otherwise zombies are spawning a mile away and then walking/running to you.