Don't let Lippert off the hook that easy - some of their failures have been inexcusable, regardless of how rare.
I did tow a boat with Lippert frame and it turned out OK, but remember it isn't just towing in a straight line. There is considerable side stress on the frame when turning in town because of the excessive length of I-beam behind the axles. You don't have that on a standard vehicle receiver hitch. In some turns, the rear trailer can be almost a 90 degree side pull. The rear drag wants to pull sideways on those thin spring hangers. Might consider strengthening them.