You have to put something on the inside of single hull trailers to cover the rough interior surface. (In the molding process, only one side- the side that faces the mold- is smooth and shiny.) Common lining materials include marine headliner, vinyl covered foam, quilted vinyl, paneling, and yes, carpet.
In many cases “carpet” is a bit misleading. The product used by Scamp
, Weiscraft, and others is actually a marine headliner. Unlike floor carpet it has no backing, making it light
and slightly stretchy, ideal for lining a curved surface. To my knowledge, the only manufacturer that puts actual floor carpet on the walls and ceiling Is Casita
But you may be thinking of double hull designs like U-Haul
, in which the interior is formed of separately molded pieces of smooth fiberglass gelcoat. That list is shorter: U-Haul
, Happier Camper
, and Parkliner
(the short-lived 16’er). .