Just finished a similiar modification to our 2016 28 BHBE today. I used this TV mount
and secured it to the backing with a dozen #12 1" wood screws with a flat washer under the head of each so that they would not pull through the bracket. I've read in other place that the backing board is made out of particle board. Not so on mine, it is made of 3/4" plywood.
Also, be sure to REMOVE the mirror before beginning the project. It is held in place by 6 screws in the TV opening. Some of the screws penetrated the back side of the plywood just a little bit, so I took my Dremel and ground them smooth before reattaching the mirror. The finished project turned out well and seems solid, but I'm still not sure about how the whole swivel is attached in the cabinet.