I picked up some automobile wheel well LED light bars to add to my kids' trailer for attention-grabbing effective.
I chose these LEDGlow wheel well lights because they were flexible, waterproof, multi-color, and a simple, single power source design. I had been looking at another kit that actually used 12v for the controller, and a separate 5v supply for the LEDs...stupid.
To power these, I simply bought a couple of 8 battery cell series holders, one for Ds, another for AAs, since I didn't know what the power consumption was going to be and wanted to use the smallest batteries practicable. I've only used the D cells so far.
The light kit was straightforward; 24" light bars plug into a distribution block which itself plugs into a control box with a 2 wire power lead. The control box has power and mode control switches on it, but the whole thing is controllable from an included remote, too.
I bought a simple, 2 wire-to-5.5mm female plug for the control box leads, and that plugged directly into the male connector from the battery pack. Very simple, and it seems to work fine so far.
I threw the battery holder, the distribution block, and the control box into a small Tupperware box and put it in the back of the trailer. I routed the wires for the light bars along the frame and into the cabin and plugged them in. The light bars themselves I just used Velcro to attach to the frame for the time being; we'll see how it holds up, but I'm hopeful it will be just fine.
The shakedown ride and time spent futzing with the various settings amounted to about 30 minutes of continuous runtime, with no signs of fading or problems. I'm running alkaline D cells right now, but based on some battery test results over on the Candlepower forums, am prepared to go to NiMH rechargeables if I don't get satisfactory run time out of these. (What would satisfactory be? I dunno, but I'd be happy if I got 3-4 hours in this scenario; I rarely drag the kids around at night for more than 20 minutes at a go, with the occasional bike fest night ride of an hour or so, so 4 hours would be low, but roughly 12 typical rides, which handily covers all of the downtown summer festival movie nights.)
Here are a couple of brief video showing the general setup and some of the many, inscrutable flash modes. You can see how the LED bars wrap around from the rear to the sides, giving good visible coverage: