Ive used the ones with the cams on my old 31" tires they fit tight and we still used bungees just because.

  Think about how hard you have to pull a bungee cord to make it stretch, and then think about it trying to hold against the weight of the tire chain multiplied by the centrifugal force created by the rolling tire.  If they don't stay in place then they are not fitted to the tire and they need to be fixed/adjusted.  If you've got three or four links loose at the ends of the side chains, then a bungee to pull it inside the tire is fine.