yeah it took me a number of tries, i saved often because sometimes the battles would just go wrong
basically first pump out marines and scv's
each choke point is blocked by 2 bunkers and 1 supply depot in between them, i know you dont like to "turtle" but this strategy is amazing vs computer since it makes the zerglings ineffective
i build a few more turrets next to the already existing turrets, and like 1 more turret to the left most side
you can leave the upper ramp bunkers unammed, no one will get in there
assign at least 1 SCV to each choke point, and assign more once you get a chance, i had 3 by the end of the mission at each end
2 bunkers + 3 scv's was auto mode for me, i didnt even have to worry about base saftey.
while this is happening get enough units to save the two stranded marine groups (there is also a third that will appear later on)
then i would patrol that arc of land in front of your base so that more zerg dont spawn, and pump marines/medics unitl you get atleast 1 full control group.
i attacked the bottom left base first, making sure to let an "attack wave" pass, then i charge!
that base gives you 3 hatcheries, then rebuild (i proably lost 50-60% of my army) and go for the base to the top left,
i got it with about 2 minutes to spare