The way trailers are built the rug or floor covering is placed over the complete floor as a starter. The plastic is put down next to protect the rug during construction. It is cut out in the exposed areas before delivery. It should be completely removed to allow the rug to breath but is never removed.
Do not install it during your rework unless you are a bean counter and subscribe to their train of thoughts.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles