I guess I'd need to try something like that. For now I was trying a more traditional turtling approach where I build two additional bunkers near where the existing two outer bunkers are (because one bunker doesn't seem to be enough per entrance), and a couple more missile turrets in the middle, and put a builder unit and a medic near both sets of bunkers so they repair them when needed.
Defending on this mission isn't too bad, even on Brutal.
Some things to do:
-Get your SCV mineral mining to max. There is an indicator over the CC for how SCVs are mining versus how many are needed for optimal mining, and each refinery has a similar counter for that refinery. Getting your mining going takes precedence over pretty much everything else; if you only have 50 minerals, then use it to get your Command Center (CC) back to building instead of getting your barracks back to building.
-You've got two barracks. Put a reactor on one for double marine production and put a tech lab on the other for medic production. One rule of thumb is having a medic for every few marines (3-5). These should be producing units at full capacity at all times (except maybe early, while you're still getting your economy going). You should have a ball of marines and medics start accumulating in your base as the mission progresses, very quickly outgrowing all space in your bunkers.
-Slip in the Engineering Upgrades when you have the resources to start the upgrade and your buildings are all building.
-Just abandon the low ground; salvage those bunkers to preserve the resources and focus your entire defense on the upper choke point. Build 3 bunkers on either side of the ramp (at the top of the ramp), with your extra marines milling about at the top of the ramp in between the bunkers. All 6 of those bunkers should be close enough to shoot at the ramp and most of them should be able to hit at least some units on the low ground leading to the ramp.
-Add turrets at intervals along the edge of the high ground to clear mutalisks looking to bypass the ramp. Build them in groups of 3-4; too few turrets in the cluster may lead to them being overwhelmed. No need to use bunkers if the walkers can't get there without going through your front door.
-After your mining is at full capacity, build some extra SCVs to stand near your defensive structures and auto-repair them. Make sure to pair off the SCVs so they can heal each other (mutalisk shots may bounce to them). If you have no need to push out, a pair of medics with each pair of SCVs can also take care of that healing. You can set some medics on patrol to cover multiple groups of repair SCVs. As you mine out mineral clusters, you can move extra SCVs to help repair. Each "cluster" of defensive buildings should have its own SCV pair (so a pair for each group of 3 bunkers, for example).
-Make sure you move out with a sizable group of marines, if you do move out. Keep the 6 bunkers full and your base should be fine for most of the mission.
-Add an extra bunker along the left side of your base on the high ground; a creep tumor sometimes shows up down there.
-Keep an eye on your supply, and build supply depots before you hit the cap. Build them on the back end of your base, lower them after they are built, and forget about them. Come to think of it, you could throw a few down at the top of the ramp too, and just lower them when you need to move units out; I've never done this (remembering to raise and lower them is yet another micromanagement task).
-Remember that zerg units move faster on creep. Take out the tumors.
-Remember that the spine crawlers will start dying if the creep degenerates under them (so they are no longer burrowed on it)! You can kill the creep tumors and let the spine crawlers effectively starve to death, though this takes awhile. The hatchery makes creep, so crawlers close to the hatchery can't be starved without destroying the hatchery.
-Knock out Nydus worms whenever you can, especially if they show up near your forces while you're outside your base. They bring in extra zerg units to throw at you, but there is a short time delay where you can kill them before they start spitting out reinforcements.
-When the timer gets down to about 5 minutes, finish up whatever you are doing and pull everything back into your base. The non-stop assault is coming shortly.