I built mine out of 1 1/2 4"x4"x48"x20' cattle panels.I used 8-6.5" tall T-post. I made a bit smaller for more rigidity and less chance of a big hog getting a running start to plow it over. It worked well when I caught 150 lb boar a few days later. I moved it since it was right by the only water source on my property at that time.
I used a stick about 16" long to hold the "door" open and it was under a good tension from the arc of the trap. I cut left a long end on each of the horizontal stays so it acted as a locking mechanism so a hog had to really run hard to push it out.
I always put brush in the entrance to keep deer out and it has worked well for me for the last 18 yrs. Hogs will root under or through it.
You can see my trip string as it run back to the stick in the door.
Not the best but it worked for me.