I've added a 12V
cigarette lighter port to each corner of my trailer underneath the cabinets, right next to the reading lamp. No USB ports in my year trailer, so I also purchased a high grade cigarette lighter to USB adapter to provide me with these, (2) 2.1A USB ports.
Remove the speaker grill to get access to the 12V
wires feeding the reading lamp.
Note, while the reading lamp itself has a very thin wire, the wire it ties into is very substantial and there is no concern of overloading it.
I used household wire nuts and taped them to combine all of the wires together (Lewster would not approve). The area near the radio was the most challenging due to the radio encroaching into the area where the wires are.