I'm cautious of using ratchet straps - if you do, make sure they're tight and won't rub.
We use ratchet straps to hold the gear onto our roofrack. On a trip to Bris, we had both camp chairs up top in their bags. The straps must have been just not tight enough, and vibrated in the wind. End result - both chair bags were completely cut to shreds in a couple of hours, and the paint rubbed off the chair legs. Doesn't worry me - they're just chair bags, but I'd hate to have to replace the cover on the camper because of it.
Back in the real world, the in-laws run a ratchet strap from toolbox to tailgate on their camper, and find it works a treat. They've never had a problem, but always ensure that it's very tight.
Good luck!
Matto