Ok, we took two 6’ sections of 3” x 3” x 3/8” angle and we welded one piece to each side of the frame after we removed the stock axles.
Next we marked the square notches that the old axles sat in onto the new sections of metal using a square making sure they were marked at EXACTLY the same fore and aft position as before.
Then we put the axles into the new notches and drilled out the new mounting holes in the new sections.
This gave us a three inch axle lift, and it allowed me to strengthen a weak spot in the frame at the same time. The fix has worked perfect for me for some time now, I got a much needed lift and by jacking hard on the rear of the trailer before welding the new sections in place I was able to fix the rear sag in my trailer. Win/win.