There are exhaustive threads on both of your questions in the archives, go
here:

http://gerry.vanagon.com/cgi-bin/wa.exe?S1=vanagon

Lots of info on both things. You will find web pages with pictures,
diagrams, etc, at least about the aux battery.
The list vendors sell a kit for the gas tank, such as:

http://www.vanagain.com/  look for gastankkit1

or

http://www.busdepot.com/  look for TANKKIT1

... there are others, of course.

Good luck,
Robert

----- Original Message -----
From: "carboncow" <feller@CARBONCOW.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, March 11, 2006 10:31 AM
Subject: Wiring in 2nd battery on Westy..

> So when you guys add the 2nd battery and combiner/relay system I am
> curious
> to how the subsystems run.
>
> Are the wires on the main battery that run to only unique subsystems like
> the light in the back, 12v fridge or stereo that can be moved over the the
> deep cycle now? Are the isolated subsystems or does the wire from the
> battery run straight to the main block under the dash?
>
> Do you have to rewire independent system to now run off the deep cycle to
> keep it isolated? I noted my dash stereo stays on with the ignition off
> but
> I have yet to test my theory that some of the 12v items run separate from
> the standard ignition circuit.
>
> Does the factory alternator have any issues with trying to juice up the
> starting and the deep cycle for anyone? I don't know the amp output on the
> factory alternator.
>
> Shawn