A typical “back drop to trailer” is a fabric panel used on “rise above” canopies.
This vertical panel closes off the gap between the elevated top of the canopy frame and the trailer roof.
A zippered connector for the back drop is standard on a Larsen “rise above” style canopy. Another method of filling this gap is with a tilt-up marque panel. These are usually framed metal panels that can be hinged on the roof.