Correct the Superlite models were mostly affected. Sagging side walls were also a big problem on those trailers. Had an 04 Superlite and was nothing but problems.
From what I remember most of the frame issues were in the lightweight line. I had an FS 2600 and had zero issues with the frame. I had several friends with FS3000's and they did OK as well.
They all have the potential. I owned a 2002 FS3000 and never had an issue. But I was careful when I went off road to make sure I wasn't bouncing the tongue really bad. Just check all of the welds/joints for any cracks. Awesome trailer.