The best strategy I found for the Bowl is here:
http://www.youtube.com/watch?v=10CpbQ2XIxk
You build up to the Drone Tech, add some Energy Collectors on either side of it and the city. Then, build two Mortars on that top level.next to the Drone tech. Then, add two SAM sites. (Don't forget those!)
The Mortars hold back the spillover. As you build more Energy Collectors and get more energy you build Blasters and move on from there with whatever you want to do. (You should expand your network of Energy Collectors in the bottom bowl and the levels up to the top once your have a good solid defense to hold back the Creeper.)
I only watched the start of this video. I just wanted to know how to get started and how to stem the overflowing tide of the Creeper at the beginning.
I can add that the Drones are a lot of fun. Their bombing helps you advance by clearing out sections that you designate.
