Given your updated info, I would be inclined to get a good roof rack.
I didn't screw around buying any fancy boat attachments, I just have a basic Thule with locking bases.
The Thule rack system is stupidly expensive but it fits the truck well and provides a secure method of transporting a canoe or kayaks.
And after installing it and removing it about 18 times, it left no damage or souvenirs on my truck.
IIRC, I paid about $900 Canadastan dollars about 2 years ago.
I have a 15' Carbon Kevlar canoe and not willing to gamble with a POS cheap rack.
If your kayaks are polyethylene or not too expensive, you might consider a cheaper rack.
Plop the kayaks on top, before loading the box. Toss 2 pieces of webbing with cam locks over top of the kayaks to secure them to each cross member on the rack.
I bought several sets for a few $ from Dollarama, they were exactly the same as the $16 set from Canadian Tire.
After loading the box, use a single loop of rope (about 4' long approximately) through the bow & stern grab loops, passing the loop through itself to create a single point of attachment. One loop on each end.
Connect the rope loops onto a V shaped set of webbing with ratcheting cams. Anchor the webbing under the bumper. I use the holes in the frame at the rear.
The V-straps were crazy expensive, I've had them for many years. I'll get pictures and post.
I'll try to find some pictures but likely only have canoe pictures using the rack.
If you're interested in learning more about using this type of system, I have a couple of other tips to save grief and improve your travel enjoyment.
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