If your wiring system in the trailer has a ground wire on Every receptacle back to the panel and you want GFI protection I would go with the breaker. Less money.
Lost of the early trailers only had 2 wire receptacles and if they had a ground connection it was to the trailer body. Not a reliable system when considering GFI
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