i'll not speak for yer set up. but it's very close to the way i tie mine up on the roof.
your lucky. looks like you have more leeway side to side. mine sits right on the edge of the roof. so i can't afford it to move. i'd say if it moves 2 to 3'' i'm off the roof on that side.
i don't have a pic of my criss cross straps at this time. but easy enough to describe. i had problems with the strap in the center. it'd slide rearward and get loose. this i couldn't afford. i found my option though. though i doubt it'll work for you. i got my canoe used. and whoever had it before me added oarlocks. they're located just slight aft of where my center strap is. my solution was to put my s hook right into the oarlock. my s hooks fit perfect. then crisscross.
i just have clam shell type straps. they're ok for my 22 mile trip to the lake. however if i had to go further i think i'd go ratchet or at least some strap that locks in place. the clam shell type do loosen with time and road vibration.
this set up for me works well. i don't go 65mph. but i'm sure i've had it in higher winds that that. going 45mph on the truck into a 25-30 mph head wind. so that's 70-76 mph winds. it stays put.
so my suggestion is that for the center strap, is to find something solid to mount it to in the canoe. wrapping the center strap around the canoe didn't work for me. going to the oar locks does. it feels solid when strapped down. i see it stressing and shaking in high winds, but it don't move. though i will say imho, 55mph w/o wind it works well. i start getting to 65mph and i start to worry. though i've no reason to as it's so far stayed where i put it.
btw, the second pic is when i first got it. the purple mat didn't work. the canoe foam blocks in the 1st pic do work. these are what i use.
. though i'll date me too, i remember too. 1st boat i delt with was pulled by a '67 olds 98. worked every bit as good as a truck too.
