Depending on your alternator and sustained current draw from the amp, it's possible that you could draw several hundred amps from the front battery. If all of your batteries were in the back you're limited by the current output of the alternator so you don't nave to worry about exceeding that number.
You'll probably be fine with a single run, but make sure voltage stays above the resting voltage of the batteries and fuse the wire appropriately. If you happen to have enough wire to do an extra run or it's not that big of a deal to do so, add another run. You won't need more than two though.