I use Yakima racks on the camper shell of my Toyota pickup. I used pool noodles when they were first installed, but they only lasted one season and now I've got pipe insulation held on with zip ties.
Usually, the Yakima cross straps are more than enough to hold my Quest securely at the average SoCal freeway speed of 80 MPH. For larger boats, I use the cross straps and a bow and stern line attached to the front and rear bumpers. You can get these ratchet-type tie downs at a hardware store for about $10/pair.
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