Actually, I bought a used steel trailer off Craigslist about 3 years ago and pull it every weekend. I had to do the routine maintenance stuff like tires and brakes etc but it has very little rust.
Unfortunately, the lady that owned it was ill with brain cancer and was selling everything she could sell.
I do agree with Joe to a point, in that I looked at a lot of steel trailers that were close to junk before this one came along.
Figure out what you want to spend and see if something comes along that you think you can live with.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.