I use the top rails that run down either side, underneath the rider's seat.Warnings: do not hook the straps to the bike too low, below the center of mass, or run unfastened straps under the rear subframe, make sure they are actually hooked to the frame.
Ask Skooter G why these things are a bad idea. I think he had some scary photos of a bike that flipped while up on the straps with no rear wheel or suspension.