This is a pretty good kayak holder. I've transported a Seaward 18' tandem kayak on these and the fit and solidity was reliable. Comes with one pair of slings.
They fold over easily, so they don't look like bunny rabbit ears on your vehicle when you're not carrying your kayak.
I've used it but 3 times.
https://www.canadiantire.ca/en/pdp/sportrack-folding-j-kayak-carrier-0401167p.html#srp
Email is best to reach me, pick up is in Colwood near Royal Roads.