I've got friends towing cars/jeeps behind their 5th wheels (double towing) & have been all over the country without any legal issues. Saw 2 identical 45' motorhomes towing jeeps towing trailers with their ATVs on the trailers, had to be 80-90' long. Your actually just towing your boat so unless you're driving like an idiot you should be fine. The simple answer is yes there are restrictions state by state & you'd have to see what it is in your state, but as I said if your properly registered, lights work, have a legal towing system, & aren't driving like drunken sailor you should be good.
Danny & Linda
Sold our '13 Thor Redwood 36 FB
Currently RV & truckless