Will the stock speaker wiring run 45w RMS?

[sqcomp]

You could easily use the stock wire...

BUT

Think about proper termination of the wire and resale value when you want to sell the car. Why? What happens when you want to plug the OEM speakers back in...

Be careful is my point. Don't start hacking the OEM terminations off the lead in wires to the speakers.

Leading the wire through the door boot is fun! :P

A hangar is definately a way to do it. I don't use a hangar for two reasons, one is that is could scratch the paint, two is that it is conductive...you just never know when you're going to ground your flux capacitor in the Yaris do you?

I use what is essentially a giant zip tie. It's 24" long and flat. It snakes pretty well.

I've snaked tekflexed 12 gauge wiring through our door boot several times. It just takes some patience.