I use a web strap with a plastic buckle that clips to lock it. Its adjustable and the ends get a screw with a washer to secure the strap ends to the wall . The buckle ends clip together in front of the screen and do not scratch the screen . You could add a thin seat cushion for a lawn chair if you desire, to protect the screen .
I do it this way on all my tv's in my RV's for the last 14 years.
I have used 2 straps in vertical positions and this past time, i installed one horizontal strap on both my tv's. Both vertical and horizontal positions work. Bought the straps at Walmart in the camping section.