Yes, we were one of the persons who has done this. We added cornering lights to the rear corners of our Montana to improve driving visibility of the rear of our rig on turns at night or in bad weather (the inspiration was when we had BOTH and we were navigating trees). Only being able to see half the rig under these conditions made us real nervous especially when backing up. The lamp assemblies were purchased at Pep Boys in the trailer/towing section. They are also available at other auto and RV supply stores.
The lamps work off the running lights (no blinking) and are positioned so that they tap off either rear lamp's running light. I drilled a hole in the side of the trailer and was able to run the wires to the back lamps (remove the rear lamp assemblies to get a better view).
On the passenger side the wire runs into the interior of the rig inches above the floor, then out the back. Wire molding covers and protects the wire in the interior. On the driver side there is a triangular piece of the wood that was removed (hides the water fill connection from the rear living room) and was able to drill a hole at the side and the rear to get to that respective rear bulb. The running lights are then tapped off at the rear lamps. Test the connections, then when affixing the lamp assemblies (ours took 2 screws each, DON'T forget the sealant around the screws and the assembly before mounting to the exterior, which should be clean. You should not seal the very bottom center so if any condensation gets in there the water has someplace to go. Then a wet finger to smooth and remove the overflow and enjoy!
Here's the link for the finished look. Pictures were not taken during the process because we were not MOCers at the time and didn't think to do so:
http://s658.photobucket.com/albums/u...0my%20Montana/
If you have additional questions feel free to PM me.
This additional post is from someone inquiring about making the rear lamps (and center side lamps) blink in unison but we did not feel the need. When changing lanes, since the truck goes first the autos behind us will get the message as the trailer with its rear blinkers follows (a trick we learned from truckers - they don't use cornering lights.) It would not be that much harder to use a running/blinker style lamp assembly, just another tap of the brake/blinker wire on either side is all.
http://www.montanaowners.com/forums/...=marker,lights