I have a 16 foot canoe - due to the design of the front it has to be angled just right at the front, to high at the back and the front will rub the roof. I tie it down to the back ontop of the tailgate and strap it to the hitch you can strap it to a hook in the box but I need the space and I don't tow. I use a back rack and straps, all you need.

This is the only pic I have: