The 2nd trailer takes a ton of stress when you double tow. I think it is because the connection point is so far back behind the first trailer axles.
I've double towed since about 2000. In that time, I have broken the hitch on the back of my trailer, broken the weld on the tower that holds my boat winch, and broken the weld that holds the pin on my brake away tongue.
In 2014 I had the rear of my 5er reinforced, along with the hitch. A welder reinforced the frame of the trailer all the way forward of the axles, and put on a very heavy duty hitch.
I'm done towing my big boat, but still tow a 17' Ranger.
Anyway, keep a close eye on all potential failure points. They are under considerable stress.
Glad it ended well for you.
