Lots of places to pick up 12 volts - as long as you don't need much amperage.
I usually look for the closest light switch or surface mount light. Get a handful of different size butt crimp connectors and a (good) crimper and go to work. Easy to remove the connector and add a third wire and install a new connector. Sometimes, like in a slide, surface mount conduit makes a neater installation and is much easier than fishing a wire through the wall.
I haven't tapped the light circuit over the sofa (yet) and usually get power from the little cabinet above the TV. Still trying to figure out where to mount the plugs - I don't think the bottom of the cabinet is deep enough.
I've installed half a dozen of the USB and cigarette lighter plug socket things from Amazon. Even easier in some cases, I have an inverter for each TV and both of them have USB ports. No more often than we dry camp these work well.
FWIW, I attached my trucker antenna to the ladder then ran the cable over to the backup camera mount through the split loom that I attached to the exterior to run the video and power wires. The camera is powered from the truck and I fished the antenna coax through the hole under the camera and brought it out in the cabinet. There is also a 12volt wire pair for the camera, but they are pretty light wires and I don't use them. On the rare occasions that I use the directional antenna on the flagpole, I bring the (fat) coax through the slide seal and there are several power sources within reach for the cell booster.
