BigTime, I was at 14% tongue weight too, so I didn't think that a little added weight in the back would hurt. I mainly wanted a "trunk" to keep the generator out of the weather and a place for the blocks, cords, hoses, etc. I need to get re-weighed at some point and see how the weight re-distributed.
If you are going to haul the bikes on the back of the TT, make sure you have a sturdy structure attached to the frame and not just the bumper. It's not the weight of the bikes per se but the bouncing effect going down the road. If you ever sat in the last row of the school bus on a bumpy road you klnow what I'm talking about.