Originally Posted by kengore
Wind resistance at 60mph puts incredible stress on things, ever seen a roof top matress folded in half as it flew down the highway? Be kind to your new toy and transport it rolled up. You even get better gas milage that way.
All of this is absolutely true, and I'll add one more problem you will encounter with a raft on the roof rack. The air will expand and contract with the air temperature and sunlight, so you might start out with a properly inflated raft, but soon find it going flabby and flapping in the wind, or worse, overinflating and bursting. Don't do it!