The acorn nuts for the tail lights are under the carpet. You have to feel around for them, then make a small slice in the carpet to get to them.
Another suggestion, you might want to reconsider the LED bulbs in your trailer. I friend of mine tried them, and ended up going back to the stock 1157 bulbs. The LEDs were OK if you were directly behind the trailer, but you could not see them if you were even just a little off to the side. Apparently the reflectors were not reflecting any of the light off of the LED, so they were just not bright enough.