It is one thing to consider a couple of hundred pounds on the back of a trailer, like a generator, but to put 1,000# plus on the very back of a trailer is an accident waiting to happen. Don't do it. Even a couple hundred pounds can cause serious issues if the frame, axles, axle location, tongue weight, etc. isn't taken into consideration.
If a trailer was designed for this situation, it would have the axles mounted further back than what you have. My guess is that the frame isn't strong enough to begin with. If I was a betting person, I would bet 100 to 1 that the frame isn't appropriate for this load. In fact, I can't think of a TT that I've ever seen that would take this load.
As far as the "engineer" goes, there are some really good engineers out there. There are also those who think that the degree that they have makes them an expert in everything, even those things that they have never worked on. The engineering advise that was given on this project is from someone who doesn't have a clue in what they are doing.
Again, Don't Do This. It is bad enough to subject yourself to the obvious failure that is going to occur, but there are other people on the road that may get hurt. Also, don't use a mechanical devise such as a high dollar WDH and anti sway system to cover up this obvious problem.