I did my decking with clamps around the frame so I didn't have to drill any holes. The rack in the rear is mounted to existing holes in the frame. I had to drill two holes for the front rack.
The boards on top of the racks come off with two bolts each and I can put longer boards on to enable me to carry two canoes side by side.
The canoe straps are not real tight. Their purpose is to prevent wind load at highway speeds from pushing the canoe backwards.
I tied one of the seats to the rear mount to prevent the canoe from sliding forward.
I'm see no issue with bending the mounts. They are pretty stout.
Zulu