I'll just focus on this bit because it's the only part I had a comment/reply come to mind quickly for.
Don't hold still. You can use almost any old prefab if you have room to run around so they're all beating on different blocks and pathing to different places constantly. I've pretty much stopped creating my own fighting space from scratch, unless I'm with others that insist on doing so, in which case I put down some perimeter obstacles to make the Z's pathing as expensive as possible. (slow down their progress with back-and-forth laterals, etc.) That's mostly what I'd do to reinforce a prefab, too, for that matter. I've come to really like wooden bars.
