There were several factors involved that contributed to the lay over. First, the center of gravity was to high, second, we were on a section of the trail that was quite steep and off cambered on the left side. And thirdly, the trailer is to heavy for the stock suspension. The trailer went over a rock on the left (down hill) side, and when it came off of it, the suspension compressed enough to tip the scales in that direction and the trailer went over. And yes I have trailer brakes, unfortunately they couldn't help in this situation.
Thanks for the info. These otherwise unfortunate events are a good opportunity for me to learn about using my trailer off road.