At 18:21 EOC transmitted the box assignment for a structure fire at the given address. With an engine crew in house Engine 731 was on the street w/ a crew or (4) four at 18:22 under the command of Asst. Chief Dorey. Medic 103 arrived to find what was believed to be an outbuilding well off with exposures. Engine 1 arrived to find as reported & the crew stretched to the rear of the address & began extinguishment. Engine 831 arrived 2nd due & secured water for Engine 731 & stretched a second line. Crews got a quick knock on the fire & began an extensive overhaul operation. Overhaul reveled a 5th wheel camper trailer that had been converted into a home for several cats, in which numerous had perished in the blaze. Crews operated for apporx. 1 hr. before picking up & returning to service.