phorid flys help

Do you have any plants and flowers pots inside the trailer? They can lay eggs in the top layer of the damp dirt. By adding a half inch of sand on top. The top layer of sand will dry out after watering. Any eggs layed in the sand will die and not hatch out. They need a damp environment to gestate and hatch.

You might also place a couple small containers out with some apple cider vinegar and a few drops of soap. I use a couple of short and fat pill bottles that hold about 2 to 3 ounces with about an ounce of vinegar in each of them.