Based on my UK right hand drive car.
Battery on the right hand side of engine bay when view from in front of the car.
Just behind and little down is a openning with a big rubber washer and there are already wires running through. This might well be back to front on non UK cars but the same still applies.
Feed your 4AWG through, it should come out on the other side about 12" from the floor.
Once all carpet and trim is lifted, this can be run straight to the back.
Fuse both ends of this cable. FUSE IT OR CIRCUIT BREAKER IT but don't cheat.
RCA should be run down the middle or the opposite side of the car.
If the path of a RCA and power or speaker cable must cross, they should be at right angles to each other.