My main problem is finding ones that stay on. The lights pull so few amps that the pack thinks the phone stopped taking a charge.
Most 120V to USB charging bricks are continuous voltage at 5V. Alternatively, there are 5V transformers readily available. Also, all ATX computer power supplies output 5V through one power lead.
For a 6' LED light strip, I'd power it with the trailer's 12V system. Should be almost unlimited reserve power for a small LED strip and you won't need anything else in the circuit except a fuse and a switch.