Is your battery in the trunk? Are you going to run an alternator?
If so how many amps will it be sending 15' or so to the batt.?
I think I use a 4 ga. wire for my alt. to batt. in trunk. 100 amps could melt a 10 ga. wire 15' long.
There are sites or books that tell you what gauge wire for how many amps going what length.
Don