All the sides are gone - but the screws are screwey

Heavy persuasion popped off the front and last piece of the grain box this afternoon. I have this 6' long heavy duty "persuader" pry bar that we typically use only to break up ice in the spring time... Well today, it got a work out prying the front piece off the flatbed. Again, I'm not convinced that it was welded, but darn was it ever stuck! In fact, the metal sleeve that the bolts went through were pulled off with the front piece!

Just the flatbed left!

Now, it's on to the flatbed wood. Here, I hit another obstacle. The first screw I tried to remove burrowed deeper into the wood no matter which direction I tried to turn it. The next two ended up rusted and could just be picked out with my fingers. So, what to do? After talking with my former wood shop teacher father, the solution is to either sawzall the screws from below, or pry the wood off from below. That'll be a project for another day.