You will soon find that companies that make these products use two types of fastening methods. The most common method you will find is the use of belts- these are usually found in the more affordable options. Belts are great because they are relatively inexpensive and easy to adjust, but the problem with them is that they can break easily- especially when the road becomes a little bumpy. Bungee cords, on the other hand, are slightly more expensive but a lot more resilient.
The can be a little bit of a pain to get them to stretch to fit over your boat and onto the frame, but that effort will be worth it when the road becomes a little bumpy. Not only will it securely keep your boat in place, it will also keep it from slipping off- which can be a problem with a lot of the best options. If you really want to make sure that your boat stays securely in place, and you don’t want to risk dealing with faulty fasteners, it might be in your best interest to invest in bungee cords before your trip- which isn’t usually all that expensive.