I don't remember if I have photos with the chains, or square tubing. I will have to look.
There can be lots of side forces on any extension. Everytime you turn, you will have side forces. The longer the extension, the greater the force. The side force can be from hitting a hole in the road or many other possibilities. They are more obvious in a trailer that is not properly loaded, and the trailer whips side to side. I have never had a problem with the loading of my Samurai when flat towing, but have hot more than one hole, and many train tracks.
I prefer the side chains (or equal) with any extension over 18-inches. Hopefully, it will always be overbuilt. In flat towing, in my opinion, the extension only has to be heavy enough to pull your towed. If it does not stretch and break, why a solid bar. Just my opinion. I see no reason to be concerned as to how long the hitch extension is when flat towing. That is if you have chains (or equal) going side to side.
I will look for the photos.
Wayne