Sorry, didn't mean to imply it was being used in a car. It's not. I'm using it to trip the latch on a chicken coop door. (I don't like getting up at the crack of dawn to let them out.)
I already have 12v power there running the electric fence. Nothing else will be connected to the actuator, just the arduino.
I like the transistor idea, I'll look into it some more.
I don't think the actuators draw much current, but I will see if I can dig up a spec. There was no data sheet in the box, but it was $2.99 with free shipping so I am not complaining