Many 5th wheel RVers that travel in northern Ontario pull a boat. I asked my dealer about it and he said that he would not recommend not recommend anything bigger than a 16 foot aluminum. I have seen a lot of guys with 30 footers pulling 17.5 foot full windshield aluminum boats.
Most I have spoken to reinforce the rear hitch supports. I do not know the specifics. I would double tow but with a 16 foot I would be at 71 feet and my wife says no. My truck is not the limiter.
Due to the swing out radius of the 5th, the boats seem to track pretty well (does not cut corners).
I would recommend an anti sway if you are going to do this. Good luck.
2004 Ford F550 6l Lariat SuperCrew, Fontaine Bed,
Link Systems Air Ride
2011 Sterling 32RL with Michelin XPS tires