A friend and I went to haul in some (what we thought was) prepared steel awhile ago. As far as I knew, it only had to be under 5 ft. So we load up a truck and trailer full of mostly ductwork and sheet metal. When we got there, we were informed that it also had to be at least 1/4" thick to be prepared steel. Great...

That's just my yard though. Yours is probably completely different. The trailer frame should be fine in regards to thickness, but you should call your yard about length