One thng I do
The long time canoe folks may disagree, but after a few trips watching my canoe be secure but still more mobile than I was used to with kayaks I just had to add one more fix. I don’t have load stops because I’d have to undo the padding to protect the kayaks and it seemed there had to be an easier way. I do the usual of a fore and aft strap over the hull and a bow line. The one diff with the canoe is that I run the bow line from one side of the hood to the other (to loops coming out from under the hood), in a triangle, with a knot in the middle to keep it from sliding side to side. With the kayak it would be a single run from bow to a strap.
But upon realizing that I could easily get at least one of the thwarts to line up with the cross bar, I also grab a strap and secure a thwart to the crossbar from underneath. Much less motion so the driver is happier. And if you do this in the rear with a long enough strap, you can run it out to the stern and make it do double duty as a flag of sorts to meet the overhang requirements.
One thng I do
Issue is it sliding off…
When I loaded the canoe on the Jeep cross rails by my self it wants to slide off the side of the Jeep! Not comfortable with that at all. Those blocks will also allow 1 person to place the canoe on top from behind and push it forward without it sliding off and possably scratching or smashing the canoe to the ground. I only have the one canoe so this is the better solution for me. I use ratchet straps on the canoe once it is on the racks. front/back and 2 in the mid section of the canoe.
I must have misread your original post. I’ve found the perfect way to load my sixteen footer without worrying about that. I square my vehicle up to the retaining wall that borders the front yard as though it were a loading dock. That gives me a height advantage that comes in handy for sliding the boat onto the bars. This may seem like a stupid question, but are you parking on the most level spot available when loading? Also, I’d encourage you to switch to good heavy duty cam straps. I think you’d be glad you did.
Redneck way or dirt cheap way.
Two pool noodles. Slit one side and slide it over your front rack and back cross member. Wire tie it down and then put your canoe on it and tie it down. It won’t go anywhere because it compresses and holds it in place without damaging your rack. Has been working for me for years.
I made a cheap rack for my suburban that will hold two kayaks and a canoe with tow 4x4’s and eye hooks. Easy to set up and use. If anyone is interested I can take pics and post them. The rack comes off when not in use. Drove to Florida and back twice from Missouri without a problem.
Both parts are maple. The bottoms are painted. The width of the cut in the bottom of the verticals is to allow the blocks to be turned to match the hull curvature. Turned out it didn't have to be that much.
Stopping sideways slide
Stuff that I mentioned above that seems to stop the sideways motion -
Using a bow line. I see sideways movement instantly and stop the car to fix things.
Triangulated bow attachment with knot in the middle - limits how much it can move anyway.
Padding on the cross bars - less slick than without.
Internal strap holding thwart to my crossbar actually runs thru the middle of an older style U-shaped stacker. As long as the strap hold, the boat can’t go any further sideways than a side of the stacker.
There are also the logical things involving how you strap it - make sure the strapping or rope is inside of vertical mounts for the crossbars. And you could always add some straps from each end of a thwart to hold a constant distance from there to the vertical tower for the rack, working from underneath. It’d take more time but it’d hold the boat.