I looked into my Winnie specs and couldn't find a reinforced place in the whole outside skin. I didn't want to transport one on the roof, because it would have to be raised on mounting brackets (I'm at 12 foot height now.)
I looked into tying it into the awning mounts, but that isn't mounted with gusto, either.
So, I came to the same conclusion that Rod offers: a trailer. That's why I don't have a kayak.
We loved all the answers. I guess that we will have to tow the truck (trailer) with the kayak mounted on top. Gas milage? Look for us on the freeways. I'll have to buy a towing kit for a Mazda (ford) truck.
Mike and Sue.