To remove the glue... Goof off, Stoner's Tarminater, Carpro Tar X, and/or clay bar. If it's really thick, I thin it out with a plastic razor blade first.
To remove the scratches... Should be able to get away with hand polishing since it is confined to a small area of the trailer. Your local auto parts store should carry compound and polish. To be as safe as possible, use this on a foam wax applicator and rub in a circular motion. Use pressure as needed.
I detail for a living and see several cars a year that had a magic eraser treatment.