A call to Heartland (877-262-8032) on Monday is going to be your best bet. While the phone team may not have ready access to a wall engineering drawing, they should be able to get with Engineering to find out where the blocking and structure should be.
Looking at the image below of this floor plan from the Heartland website, my 'guess' is that there would be some aluminum structure on each side of the window going all the way to the roof and in the center of the window going all the way to the roof. Again, just a 'guess'. In terms of actually backing, it's 'possible' that there's a piece of sheet metal under the interior wall board.
If I was installing a TV the size depicted in the image below, what I might do is find the vertical structure in the wall (stud finder, brad nail etc.), mark it out and screw to it, a piece of 5/8" plywood or MDF. I'd obtain a roll of interior wall decor contact paper from Heartland and cover the backer board I installed, then screw the TV mount to my backer board.