For years, I have a pair of rod holders with magnets that I simply stick to the hood and roof of the car, and strap the rods to. They're really great and I've yet to see one fall off. They *can* fall off - a friend has had one of his fall off.
They're magnetic and with a little bit of suction-cup effect, but they don't sit rock solid on the car, so I use them only for short moves and I never drive particularly fast with them. After all - a rod-reel-line-setup isn't cheap. I still use them a lot - especially for double handers.
I've also often, with single handers, just thrown them in the car over the seats. I have a station wagon which will hold up to a 10' rod. But the skate around in the car, and I've just bought a nice gizmo to counter act that.
Leave it to Japanese C&F Design to come up with awesome solutions to problems you never knew you had :-). When I saw this, I just had to have it. It's simply two foam things that you suspend between the necr rests of the seats that hold the rods. It's a great solution!
The back one just sit there permanently - the front one I take off. But - it's C&F Design, so it comes on and off in seconds with two snap buckles. The straps that hold the foam-thing to the seats I just leave on - they don't bother anyone.
So if you move around a lot over a day's fishing, I really recommend this thing from C&F - it prevents the rods from skating around in the car.
Have a great weekend!