Read all the posts here, very interesting! With our old 5th trailer at only 27 ft. we towed our 17 ft lund pro sport behind our trailer a lot! Total length approx 70 ft. In Manitoba max double tow is 75ft. It handled and followed very well, no swaying, fishtailing etc. I could see the boat trailer wheels in the rear view mirror. My GCVW was about 9500 lbs. so I was within my weight ratings! My old triple E trailer had a square tube frame, very solid and I installed the hitch myself, a class 3 hitch. The boat & trailer were under 2000 lbs. so I was not to concerned about stressing anything and the boat trailer has surge brakes.
Also I limited my max speed to 55 mph with this combination. Oh and another thing, in Manitoba you can only double tow behind a fifth wheel not a ball hitch trailer! If done properly and proper weight distribution it is a very doable thing!
Now I have a question, does anybody have a factory installed class 2 or 3 hitch on the back of their fifth wheel trailer (any forest river). I ordered one with the trailer we bought thinking it might be a class 2 or 3 and received it with a class 1. A class 1 is only good enough for a few bikes, generator, etc. Any other thoughts?