Please post pictures of how you covered up the window(s) on your trailer's outside door. As you know at night you can see right thru them when there is a light source behind it. I'm just looking for...
Bingo! those rods are the ones I mentioned. I can't think of a way for them to fall off. If you're concerned about the brackets staying securely in place and want this to be absolutely permanent, add a drop or two of Superglue, Gorilla Glue or similar under the bracket. The rods mentioned, come in either white or a brass color, I believe.