Vincent Meats is a home-kill service run by Darryl and Paula Vincent, who have a retail shop at the Whanganui River Markets every Saturday.
Vincent had the trailer stored in a shed with the panels loaded on it, ready to be put together when he had some spare time.
Due to rough weather in Turakina on Saturday night, no one heard or saw anything when the trailer was taken.
Vincent said the trailer had been secure.
"It was in the shed, the gate itself was a locked gate, but if someone wants something, they're going to get it no matter what.
"They definitely came prepared. They would have had to tie the panels on because they were just lying on the trailer."
It is a 2009 trailer with the registration N406H and the panels are four metres long.
Vincent has never had anything stolen from his property before and nearby neighbours had not experienced any similar issues.
Police were informed of the theft on Monday and are making inquiries.