Venango County 911 said the blaze at the park broke out about 11:30 p.m. Sunday.
Seneca fire chief Paul Marsh said no one was home when the fire erupted, and he said an investigation into the blaze is being conducted by Franklin state police. Marsh said the trailer was declared a total loss.
In addition to Seneca, firefighters from Franklin, Sandycreek Township and Rocky Grove, and the Emlenton rapid intervention team, responded.
Firefighters left the scene about 2:40 a.m.