I'm stick with Fortress Siege.
I have more 20 Berthas and still can get close to emitters. Any tips?
check his thread out http://knucklecracker.com/forums/index.php?topic=14677.
basically it says more PZ'd berthas targeting around (not on) the emitters, shields and terps
My strategy was the above as well as sprayers along with a guppy/ shield strategy to get rid of the back nests for extra PZs and less creeper being emitted. hope it helped
A month late to the party but....
I was struggling to get a nullifer to build until I moved a command node right next to where I wanted it to be built. Once built it survives as well as a cannon does in the creeper, so the occasional bertha shot to keep it clear keeps it alive long enough to charge up.
If you haven't got it yet, I hope that helps