I see that a 19" TV and bracket is an option with this model. Where would it go? There may be a backer plate behind the wall finish. Where is the antenna outlet now?
Where are you trying to view the TV from? The sofa, the bed or both? Would it work for you if the head of the bed is on the curb side (I think not because of the window)? It looks like if you mounted the TV at the end of the upper kitchen cabinet, and used the curb side for the head of the bed, you could view from the sofa and bed. I note from a photo on the manufacturer's website there is a divider wall at the end of the kitchen cabinet. This would allow a TV larger than 18".
For viewing from the bed, can you lay sideways and watch the TV from near the rear of the trailer in the location you suggest? Maybe that's why you are thinking of that spot? If all you care about is viewing from bed, I would suggest mounting the TV at the end of the cabinet over the sofa. In our Catalina, even though we could easily view the TV from the dinette, we preferred to use the bed. (That's where the wedge pillows really helped.)
If you were to mount the TV at the rear of the trailer as you suggest, you would not be able to view from the sofa. Plus, what would you do with cabinet doors?
Okay, I see you have a model 1860. Not that it matters, but I assume you removed the dinette and installed the sofa yourself as I don't see it as an option? Great idea.