Car top (SUV top) but without the bars. I actually have a yoga mat I put on the roof of my Honda C-RV and then i put the kayak on top of that (upside down) and then i use two straps that go over the kayak and through my car doors and are ratcheted down. It works really well, i have never seen the kayak move from its place or slide at all and I've reached speeds of 60MPH. I wouldn't recommend it for long drives though, or add bow and stern straps if going for a longer drive.
is it the best way? I dunno, but it works. it is similar to using those foam blocks for car tops. make sure the yoga mat is grippy.