My 16' Wenonah will not fit on the roof on the side of the AC, so I am removing center bar from it and putting it over AC.
For front mount, what is narrow, I drilled 2 holes next to skylight and bolted plank of wood where I strap the canoe.
For rear, I used factory rails with double 2x4 across what is hold by couple of those SUV rack holders.
For loading I wrap foam sleeves, from rack place again around rear factory bars and just pull the canoe over them.
I think the canoe adds to aerodynamics mounted this way, but not enough to measure bigger mpg.