I thought about size for a bit. I decided I didn't want it to wrap around too much because I was afraid it would flap some if the edge were parallel to the air flow. As it is, it's strapped on there pretty tight. A sports bra? At any rate, it was custom made. I even had a little cut out made around where the electric service enters from the hitch.
I also considered color. I felt that white would stain and be difficult to clean. Black hides a multitude of sins. It could be made out of any color that vinyl is available in. I suspect yellow is very possible.
There were three types of fasteners I could choose from. Snap, post or twist. I used marine twist fasteners, riveted on with 5/32 inch rivets, carefully drilled for depth. I slathered on white silicone around the rivets and in and around the holes and then I filled/covered the rivets with clear silicone after riveting
It's made of the heaviest vinyl offered that doesn't have a foam backing. I'm getting some cracking on the vinyl A/C cover which he attributed to the relatively thin vinyl used. I don't intend to leave the bra on all the time. Only during travel.
It was a quick job. I had to leave the trailer with him for 1 day. It turns out he was 2 blocks away. It was a little over $100, less fasteners, which I provided. I wanted him to be sure and use marine fasteners which I expect to be weather resistant.