Yea I think there might be pigs. Looks like someone left a spiral-fence type pig trap out in one of the clearings.
With a tube feeder, or gravity feeder, I assume I would want to get that off the ground so pigs wouldn't destroy it? I was thinking about building a few out of 6" PVC. Cheaper too.
The only problem I see with PVC tubes is the amount of (or lack of) corn they will hold. You would probably need to fill them pretty often.
I agree with Bassin on using feeder pens.