Well, I'm glad you posted this. Pulled out the trailer today to prep for the trip to Ishpeming Wednesday. ('05 Triton XT). I gave the axle and frame a good look after reading your post. Sure enough, both frame rails have big cracks at the rear mounting point of the axle. It was fine when I gave it the once over in the spring so it must have happened during our trip over the holidays. 900 miles each way but I bet it happened on the super rough ice/snow covered roads between Bloomington, IL and Shelbyville, IN on the way home Jan 7th. It took us 9 hous to cover that stretch and it must have been too much for the trailer. I'm traveling for work on Monday and Tuesday so I guess I'll have to get a uhaul and leave the spare sled at home.
It sucks but I'm sure glad I found it now and not the hard way! Check those trailers everybody!