I have become invincible in survival mode, and i will tell you how(only available after second-to-last mission)
Start off with a green gas factory at the top with some room for blue gas factories on its path.Upgrade those and all procedingly made to full capacity. After the first few are upgraded, make the most expensive spider factories at the top of the screen, all of which with enough room between paths for blue-gas factories.
Very engaging game, wish there was a sequel or something. A very good game overall for its basic style and should be further analysed and improved upon.
 "Robotic Emergence"){kind=icon}