If your model doesn't come equipped with one..........it's probably NOT going to happen.
There's a lot more than just buying the so-called insert as you describe it.
You'd need to know exactly what and where anything might be inside the wall location you're envisioning. You'd need support strength, electrical connections, coax connections back to your antennae or satellite....and on and on and on.
Do like others have done including myself.........place a TV in one of your cargo boxes and run the connections to there. On our rig, we have a 32" inside the "belly box" underneath the awning, and it's the perfect viewing height with our patio chairs.
Ken and Terry
2010 Georgetown 330TS being pushed by our
2017 GMC Terrain toad (4 wheels down)