Double tow is legal in Indiana with the first tow trailer being a 5er OR a TT. I've seen all kinds of combinations in my state. Usually the 2nd towed trailer is a much smaller trailer, mostly to carry ATV's or motorcycles. I have seen some folks towing a smaller travel trailer with a John Boat, sometimes with a motor, behind the trailer. Indiana does have 1 rule, the entire length cannot exceed 60 feet of any combination of tow vehicle and trailer.
Here's a good informative web site:
Click here.Yes, you can do it if your state permits it. Your trailer will most likely need to have some reinforcement done to the trailer frame for an adequate hitch so the extra weight dragging behind the camper will not rip it to pieces.
One risk though... if your camper is still under warrant, your warranty may be voided if you start welding additional framing to your existing framing. It all depends upon your specific camper if you can actually do it or not. Some campers are so lightweight, it would be death to the camper to attempt it.
But yes, people do it all the time.