Its ALMOST the same as wiring up a speaker in series... just positive run to the rear battery before the amp, then fuse (if you want) then have seperate ground wire from battery and amp. DO NOT ground your amp to the neg - terminal on the battery
Why not? My understanding is the battery is the best ground you can get since everything grounds at the battery anyway.
@Pburke
You fuse for the wire. So if its OFC 1/0 use 300a, 4gauge use 120a, etc.
Meaning have an actual ground not just to the battery. and you can never have too many good grounds so run one set for battery and one for amp