The cheapest way to do it is to take the bedroom tv and get a new stationary mount for that tv, the mount I used retailed for $19.99, then I used the cantilever mount for a 40" Sharp for the underbelly. I don't have the same model Pinnacle, but I don't thing they differ from model to model.
2012 36REQS Pinnacle w/ Reese GooseBox
Stays at Lakehills, TX on Medina Lake most of the year!!
Chevy Silverado 3500 Duramax Dually