Pretty much as the title says.
I can get it down to 10 towers, this is w/o using any missiles, but I can't for the live of me get above the 65000pts mark. best I've done was 59-someting
My usual strategy is placing a single cannon by the cores (for early damage and taking out straggling flyers. The I use the platform in the south-east corner, and let the aliens run by my towers twice. Mostly Gun and a temporal.
These are backed up by Cannon towers and a meteor on the middle ledge (just below the exit).
Any ideas, suggestions, guides will be greatly appreciated