I tried with a 12 ft Ocean Kayak Yakima racks moved far forward on a Ford F-350 Crew Cab, 6.5 ft bed. It looked like it would clear the nose of our Crusader 290 RLT when we loaded it and took some sharp test turns. After we got back from our first trip, I noticed a dent in the roof of the truck. Bummer. It must have been a compound of a tight angle and a slope that pushed the kayak hard enough to dent the roof right where the roof rack tower sits. I was lucky I didn't damage the 5er...tough fiberglass. After that we went with an Orukayak.
Don't ask me about the mountain bike handles and the back window of the truck. That was another "unanticipated modification," and why we went with a bike rack custom fitted to the back of the 5er.
I've seen pictures of kayaks on the roof of a fifth wheel, but I don't have the roof, the luck, or the checkbook for that.
You might need to consider a different, shorter boat. Good luck and let us know what you come up with.