If I was still into stereos I would use a second battery like you said. It's easier on your alternator. Or use a higher power alternator or both. Caps are pointless IMO. I left the stereo crowd around '03 when I got into operating heavy equipment, and the last thing I want to hear is noise from speakers. Use a DEEP CYCLE BATTERY and a high power alternator if you want max power flow. Hide the battery if you don't want to see it due to its ugly appearance.