That's a pretty good suggestion, I never thought of using water. How hard would it be to fill the moat in survival singleplayer? I live pretty close to a water source.
So that is my current "base" in my alpha 17 world. I had the original plan to create a moat of spikes with 4 bridges leading to my main platform that had hatches, where zombies would fall straight through and die. But i'm playing on Darkness Falls mod where nights are hordes are incredibly hard...