First, you are doing a beautiful job on your teardrop. Keep up the good work!

Now, about the backside of that pivoting TV screen, I vote for a narrow cabinet, about the depth of your wallet or cellphone or the equivalent of your home's medicine cabinet. I know you've built a place for charging, etc, but the depth I describe allows you to be flexible in whatever you decide to put in the cabinet. You might even be able to simply mount an actual mirrored medicine cabinet there; but, from the looks of your skills, I think you can make something much, much better. Make shelves inside and add a lightweight, thin door in front or whatever. Since it's a pivot wall, be certain that the little cabinet does not impede the turning. Depending on the cabinet door style, with your TV mounted on a swivel, you can turn the TV wall part way and be able to access the cabinet on the back, without turning it the entire way, especially if you make sliding doors on that little cabinet. You may find that you like using that pivot opening in the morning, to make your coffee/tea/hot chocolate on the galley counter and be able to drink it in bed while you slowly awaken to the day, especially if it's cold outside! If you decide to do that, you may want to stock the little cabinet with cocoa packets, tea bags and tea-bag style coffee bags, powdered creamer, and sugar packets as well as a few spices. Whatever you decide, you'll find the best use for it with time. But, you're right! It would be a shame not to take advantage of the flat back of that TV wall.