Your first limiting factor is the thickness of the wall, and the mounting board. The inner wall is about 1" thick, and the pre-positioned board is probably (at most) 3/4" thick. The diameter of mounting holes in a bracket will limit you also. So at first, you're limited to smaller mounting screws (way too small for lag bolts) than you would like.
As you realize, an extension, i.e. swing-out bracket adds a lot of leverage on those little screws.
Because of those reasons, we opted for a smaller (about 24" diag) flat screen that weighs very little. There's a nice one made by Axess on Amazon, that weighs only 12.5 lbs.
Like ours, it actually runs on 12VDC, uses an adapter if you want to operate on 120VAC. Also, like ours, it has it's own built-in DVD player. The brand we have has been discontinued. The 12VDC option should be obvious to any RVer. It will work even when you're not plugged in. IF you have a 12VDC outlet. Some of the newer ones do not. Here's a link. https://www.amazon.com/dp/B00BCS1EM2...ing=UTF8&psc=1
I forgot to add that we leave ours mounted and wired. For travel, I just put the two Styrofoam "ends" that the TV was mounted in the box, on the TV in the RV. The big foam "sides" effectively wedge the TV to the wall, and stop it from wiggling and shaking.