If that's your only tie-down points, I wouldn't want to be following behind you.
It may not sound like fun, but crawling under there and finding secure points at frame/suspension to secure your load is a lot better than scraping your car off a guardrail or out of a ravine.
I also run a bridle attached to the frame from my winch, and always set parking brake. Still might look into another idea based on the replies to my post.