Is there a hole drilled in it? Is there only one? This could be an extension channel for your air conditioner condensation drain hose. It directs the water away from the trailer so you don't get a dirty streak on your siding. I have seen these, but I couldn't tell you what brand of trailer they were on. Just my 2 cents worth.
"Walk softly...and carry a lot of tools!
2016 Ford F250 Super Duty Crew Cab, 4x4
2021 Palomino Puma 27RLSS