I want to add a valor 600watt/300 continuous watt power inverter to the system in my car so I can install a ps2. I'm already running 1 T1000bd and 1 p450.4 Fosgate of course with 3 12"kicker CVR's the systems demands a lot of power and to protect from shorts I have a 200amp circuit breaker under the hood. Since I planned on putting the inverter under the custom made center dash console it will require at least 6feet of wire so I've read that it will need a in-line fuse 80 amp or so to protect from surges can I hook up the 80amp inline fuseholder to the same battery post I have the 200amp circuit breaker? And what gauge wire should I use? Or what is the best recommended application?

To tell you the truth a better system is to get a power supply that's made for cars and PC's.

This site will help. wire gage selection

You just need to convert watts to amps and use an efficiency such as 80%. 80-95% may be common.

I = 12/300*(1/efficiency)

For 80% efficient use (12/300)*(1/0.8) for the current in AMPS.

Use distance and the table to find the minimum wire size.

For the single numbers 18-0, 18 is a smaller wire size. 000 is bigger than 0 and after that the wire size is in CM or circular mills. The higher number is bigger.

"bigger" means carriies more current with less voltage drop