I have the 2017 and installed one right above where the cable outlet is. If you press hard enough against the side, you should be able to feel where the backer board is. I drilled 2 holes for the screws and mounted a swivel bracket. Ill send a picture next time I'm over at my camper.
Sorry about the pic. It was of the TV in the dining area. I have also located the backer for the TV in the bed area. I will be mounting in the near future. I will grab some pics of that as well.
__________________ 2016 Wildwood 261 BHXL 2012 Ford F150 XL 5.0 L