I dreamed that one up. I was looking for a way to tuck 4 batteries in that area and still allow them to be replaced. I designed it and welded it up ahead of time and then couldn't quite get it in place without cutting part two of the angle iron pieces back off :( I ended up finishing up the welding in place. It did of course add a fair amount of tongue weight. But the Arctic Fox is pretty heavy anyway and has a lot of ground clearance so that helped. It hangs down about 6" below the tongue frame.
I used 2" 3/16" tube steel for the bottom portion and 2.5" 3/16" for the top. The rest was 2.5" angle. I drilled out some holes and use receiver pens to allow it to be lowered using a floor jack.