Make sure it is welded up well. The trap should have a floor of pig or cattle panel. It has to be staked down with t-posts, otherwise the hogs will upset it.
Hope this helps:
Portable Hog Trap Plan
Here is a good video of a corral trap:
Home-Made Hog Trap and Pen - YouTube
Hope this helps:
Portable Hog Trap Plan
Here is a good video of a corral trap:
Home-Made Hog Trap and Pen - YouTube