Copper clad aluminum is poor quality and should be avoided. It carries less power for its size and is prone to corrosion.
The only other thing you might need is some extra speaker wire depending on where you are getting your audio from.
I'd give Rockford a call on this one. Tell them you have a P300-12, but none of the wiring to it. You need the main power harness and the audio input harness.
Then you need to buy an 8 gauge wiring kit.
Will give you a tickle without breaking the bank or setting your car on fire.