Circuit in ShangriLa

Ok, so this is the circuit setup that sort-of works.

1. Do not open the 'door' near the Olympia gun in the starting area, but freely open all other doors.
By doing this, when you camp at the top of the water slide, you force all spawned zombies on the map to walk to you via the downstairs tunnels, then they must pass the waterfall, go through the waterfall-to-bridge tunnel, then either run through bridge/mud-temple, or the 'other way' toward the start of the water slide.

2. From whatever round you can, camp at the top of the water slide after you have all doors but the one mentioned at point 1. Players need to split themselves between shooting zombies at (a) the window near the water slide entrance, (b) the mud temple and (c) the hole and the ledge towards the tunnel.
Setting up any Spikemores around here is a good idea. I recommend pointing the front towards the encampment, so that the spikemore wont' detonate until the zombies are closing in on you, to give you a break and an audible warning to move.

3. When this camp is overrun with zombies, everyone take the water slide; when you get to the bottom, avoid temptation to buy anything run straight to and use the geyser, then pile onto the mine cart. Hold this position by ensuring someone is each pointing a gun at (a) the nearest window, (b) the edge of the deck overlooking the drink machine, (c) the way towards the geyser landing spot, and (d) maybe someone pointing to the farther window or facing the front of the mine cart in order to start the ride when the other players need to reload their weapons.

4. If everyone is on the mine cart when it goes, that's good; if someone is down, there is some kind of glitch at work that they will seem to 'stay' at the start of the ride until everyone lands by the waterfall, then they instantly 'teleport' to the waterfall where they can be revived.

5. After the mine cart ride, go through the tunnel towards the bridge, cross the bridge and walk through the mud to get back to the top of the waterslide; then fix up the camp for another circuit.

By keeping the debris near the Olympia, this ensures that the zombies must take the long way to get to you: from the waterslide to the mine cart, they must go through the lower map (the mines) and in reverse, the long way again.
I guess that the alternative is to not clear the debris between the waterfall and the downstairs room with the Stakeout shotgun, but it is not quite as good.

Addendum 1: I posted earlier about keeping the debris near the M14 might be the way to go, or the debris in the waterfall location. I guess though that it doesn't matter too much, only how soon you might get swamped from either direction. In hindsight, I think the debris at the waterfall or the tunnel at the bridge/waterfall is better to save it closed, although having it open is part of the Eclipse secret. This way, more zombies will funnel through the mud temple and have to slow down as they run through the mud, which is advantageous for a team with LMGs/ARs (to rack up points) or other good guns to mow down zombies from the camping spot.

Addendum 2: I did this circuit with three, relatively-nooby players and we all got to Round 22 before getting stuck down near the Juggernog machine, minecart side. Seems to be effective.