That's my brother, and yeah, it was about an 18 or 20 footer that he made slideout extensions for with taillights and markers in them. Worked well but was super low for how long it was. He sold/traded it several years ago when he didn't need that much space. It only worked because his axles were pretty far back to start with, and it was a tandem 7k axle trailer to start with.
I've put two crawlers on mine (16+2 14k) but I stacked them to do it, first one went on backwards hanging as close to the tow rig as possible, next one on top of the first's front tires till nearly putting diff on hood. It's fun to tie down that way but if the trailer is sturdy enough and the two rigs well matched, can work. I can only see disaster trying that with the actual thread topic, I did it with two full size tube cars on 40+" tires. At least the loading of that will grossly overload the tow rig for tongue weight, and will probably be over on anything shy of a class 5 hitch when loaded too, worse if the two things aren't evenly weight matched. I was towing with a crew/longbed/dually at the time so not a worry there, but still not something I'd recommend to "just go for".