Just a few tips for apocalypse setting. The first portion (say 10 minutes) is the hardest part of the mode. If you can make it through that you SHOULD be able to beat the whole thing.
Make sure to upgrade! When outside of that first 10 minutes, whenever you build something new it needs to be upgraded. You shouldn't need repair bases either: If you do, you're lacking damage and will probably get overwhelmed in some of the later stages.
Nuke stations are EXCELLENT, provided you have lots of them FULLY upgraded. Non upgraded nukes are terrible, and level 2 ones are only marginally better.
Finally, when you've finished the planet shield and most of your upgrades, start selling off your finance centers and replace them with turrets of your choice. They're not really needed for endgame, since you shouldn't be losing bases then. Good luck!
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