I had a similar deal with my trailer 2 years ago. Wanted to haul one of the Cub Cadets but the trailer just didn't look "right".. turns out the frame had cracked in two right behind the axle mount. Had quite a bow in the floor! LOL.. Had to strip it all down and replace the whole frame! Went to a friend and "acquired" the steel so the repair only cost me some welding wire and a weekend of time.

Hope your project trailer goes as well! OH, and thanks for the pictures!!