It's not predator proof AT ALL! My first tractor I built like a tank. 2x2's, hardware cloth, latches, even 2x10's all around it to keep animals from digging in. I live in the middle of several hundred wooded acres in Michigan, so I figured I'd have horrible predator problems. Then- nothing. No tracks around it, no digging attempts, not a single sign of a predator. But, the darn thing was so heavy that I could barely move it. I'd run over and nearly crush birds because I couldn't feel them under it if they were too lazy to move when I was moving it. Any non-level surface and the 2x2's wouldn't flex, and I was left with a gap between the bottom of the coop and the ground. I HATED it. So, I put it on Craigslist and built this one. I'll never go back- it works great.
The four sections are just the framework of the SCH 40 PVC. It's one big opening inside. The bottom frame just holds it together better.