my concern is mostly about unloading the tongue of your TT.
Just that hitch structure alone is doing a big part in tipping your TT back. Adding a heavy bike rack, cargo platform, or the tongue of another trailer will do even more......
and a light tongue can lead to increased sway potential.
not knowing the many variables, I couldn't begin to say with any certainty what the capacity of that thing is, but looking at your quality of fabrication I'd guess you know what you are doing and that it's pretty stout.
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