Videosecu.com has some really nice mounts. Used one in our old TT for a 19" TV. They have ones with unequal length arms which may be something you want to consider. This allowed us to flip the TV 180 degrees to view from either the bed or dinette.
We initally bought the one CW has and it is poorly made. The pivot points and sliding bracket are so sloppy, when it's extended, the TV angle changes quite a bit.
Mor/Ryde makes a really nice articulating and locking mount. Got it online for about $100 incl. shipping. Has a rubber handle on the bottom to pull down and also has a chain you can use.
Our current TT has an articulating mount that is held in place by pushing it against the wall to lock. Don't particularly like it. Don't know the brand.
If you get a mount that is not locking, you can hold it in place with a couple of velcro straps. I used a couple of plastic clips from www.theclip.com.
Clips for velcro straps I have seen new TTs at an RV show that come this way new from the factory. Not as elegant as a locking mount, but it works fine.
When your TV is fully extended on the articulating mount, that can be quite a bit of weight (TV + mount) and thus leverage on the cabinet the mount is attached to (unless attached to a wall) and could cause damage from bouncing during travelling. You may want to add some structural supports up to ceiling joists or wall studs. I used plywood attached to the ceiling to span two joists and then attached the cabinet to that. We used a 19" TV with built-in DVD player which added a little more weight too. I used a little blue loctite (not red) on the threads into the back of the TV for extra security.
Don't forget to secure the TV when packing up to go home. It's an easy one to miss...