Gjl,
As Jim said, it's a little difficult to offer any help with so little to go on... BUT here are a few thoughts...
You said you have a wall Mount for the TV... if the design is one to go behind the TV... without a swing arm... using that type of mount your going to only attach it to a flat surface... some have used a piece of plywood to attach the wall mount on.. and then some how attaching the plywood to the RV... not knowing which bedroom cabinet design you have... makes it difficult to suggest how you should do this.
I used a swing arm mount... here is the Link: Post # 7
//heartlandowners.org/showthread.php?t=3295
Give us a little more to work with and I'm sure as Jim Said... lots will offer you a solution.