If this was added to a 5er that had heavy enough axles and tires you might be OK, but no way can you do this with a TT. Not enough tongue weight is what makes trailers sway. The idea that 100 lbs back there only takes 33 off the front is way way off as it's closer to 100/80 with the Harley behind the rear bumper. I'm actually surprised that you have any tongue weight. The closest I've ever come to having a trailer take me to the scene of the accident was when I added 250 lbs of bargains to the back storage area of a 25' Airstream. Your engineer must have gotten his degree through the mail.