Well, here's one I've never seen before!

This is a really good way to handle the stresses of double towing. Copied from the dollies commercial drivers use hooking up a set of doubles or in some states triples. Removes the tongue weight stress and places that weight on the dolly.

I have typically seen these used with stacker trailers that have huge tongue weight. Saw one a few weeks ago that had an air bag assisted hitch system. I have considered one for the MH and cargo trailer but I can't justify the price.