Gas trap > Fire Trap > +1, place after every health point and every 'hero' except jet packs will be constantly losing health. I then placed a charger > emp > +2 somewhere near the center. A few drones to keep the snipers busy and finish up with upgraded blasters for massive damage on armored. B > D > C > E > A > F for general upgrades.
Note: I dunno if it is a bug or not but when a hacker disables a gas trap (base or fire upgrade, haven't tried frost) they are still affected by it.
 "Idle Hero Tower Defense"){kind=icon}
 "Scream Collector"){kind=icon}
 "Kill the Heroes"){kind=icon}
I'll unlock it for you.