You want to drill the hole right on the very end of the crack..not past it to hopefully stop it from progressing.
The crack of that size is definitely a structural problem. You will need to pull the outer snin from the trailer around the pin box and inspect the pin box area. You will probably want to get a professional to do a liquid dye penetrate test on the welds around the pin box. It there are no cracks or broken welds, you need to have a certified welded add some additional bracing to the area. There should be very little movement it the frame was properly designed.
You need to check to see if you have a Lippert frame and see if you can get any help from them or the TV manufacturer.
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