The 8ga should be sufficent as I have an 04 PT175, and upgraded to the 55 # Terrova w/IP in late 2011. I used the oem TM wiring since I stayed with 12v (same as MG oem TM). I installed a NEW re-settable breaker at the battery tho.

I have run new power wires for a bow FF and went under the livewell/under the seats storage area and floor all the way up to the front. Ran the wires inbetween the gas tank and batteries to get to the opening under the seats. You can probably remove the front deck flooring by removing the screws along the edges, just have to hunt for 'em in the carpet and remove the small front panel where the TM plug/TT switch is by removing more screws hidden by the carpet.