Sometimes I think that we over complicate things while trying to be gentle on the walls and cabinets. Most of the electricians that I see will wack a few holes with a hammer, install outlets and leave. We, on the other hand, fret about avoiding patching and painting. Another dimension is that customers don't seem to mind hiring a patch and paint person after the electrician, but object to doing the same for us.

In this particular example, you should be able to anchor 2x4's to the uprights and cover with a false back. Unless there is some other reason to use an articulating arm, a flat mount should work.

If the TV mostly fills the opening, just paint the chamber black, rather than attempt to match the wood.