We own Bromptons and want Travoy`s (but not the price) and have done some serious DIYìng in the past
so we are following your thread closely!
What we are discussing is that we would not be comfortable with connecting the towbar this high up on the B`s. We all use extended seatpost so we worry about them being over loaded already. If you do not need to fold the bike completely every dayyou could slide the hitch down a bit, not sure how much seatpost you need to insert to keep the bike folded.
Is there a way to connect the trailer to the bike instead of to the seatpost?
Do you need to pull the handle all the way out most days? Could you leave that for the days you want to transport something tall (and just secure it with some zip ties or welcro) and take the advantage of a lower and also stronger (and easyer to connect lower- like on the bike) trailer for most days? Just asking.
Really looking forward to seeing your new solution for connecting the wheels.