grounding second battery

I am mounting a second battery (Odyssey ER 30) in the rear of my 1999 VW passat wagon and plan to ground it in the rear to the same part of the chassis that the rear metal bumper is attached to. All of the stereo equipment hooked up to it (including the head unit) will be ground at the same point. FYI I will be using a pheonix gold capacitor power grid, which centralizes power and ground and makes it a little neater. Any advice on grounding this setup? The stereo will be entirely isolated to the rear battery (even going as far as using relays for illumination, ignition, etc.) and as such I figure there should be no ground loop coming from the difference in potential between the two different battery ground points. Still, in addition to a substantial ground wiring setup for the system and the battery, I was considering running a ground wire (just a simple 8awg) from the rear ground point to the front battery's ground point. Is there any advantage to this, and if so should I consider using a heavier gauge? Or should I even consider not grounding the rear battery to the car but only running a heavy gauge ground all the way up to the primary battery?   Has anyone actually done a long ground run? I'll be honest I don't like the idea of a long ground run as an exclusive means of grounding a battery or system, particularly for a battery. As you can imagine I will have an isolator in between the two batteries, and a Soundgate ICB100 (intelligent fuse), not that either of those matter to my questions. Thanks in advance for your input!destination moon

If your deck can be made to ABSOLUTELY float, then there will be no issues with ground loops... you are correct in that assumption. However, getting an ABSOLUTE float will be nearly impossible, as your amplifier's RCA shields will be connected to chassis ground through the amplifier, the antenna shield is a chassis ground... That being said... I'd rather you didn't extend your ground cable any longer than is necessary. Also, the cap is a waste of time if you haven't updated your alternator. I'd also ditch the isolator. You're gonna eat batteries, dude.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."