Gary, if you are still covered under a warranty I would have the dealer fix it. I had a rear marker light that was not adequately crimped. According to my dealer, on my trailer there is no way to remove the marker lenses/assy's without breaking the tabs. I don't know if this has changed or not since 2011.
It sounds like there is a common intermittent loose connection/bad crimp, possibly at the front/yellow light. You might be able to find the bad connection by hooking the trailer to your TV, turn on your lights, and starting in front of your yellow marker, hit the side of your trailer with your palm. Hit with firm (not hard damaging blows) pressure, to simulate road bumps. If the lights blink, you have found the general area of your failure.
If the lights don't blink, continue hitting the skin, working your way towards the street side. I don't know how low the wires are run, so this might take some time. I believe the umbilical enters the trailer under the bed near the front curb corner. There could be a loose connection here as well. Its been a while since I've looked at these connections, so I may be a little off.