Hi Donna,
The 2 battery set up in my '85 Westy was already installed
and configured when I bought it.  I had a mechanic look it over & explain
the rudiments of it's particular installation.
It seems to be set up logically:  I can take power from the Aux battery for
"house" use, without tapping the starting battery.
    However, when my engine is running, or if I plug my solar panel into the
main cigarette lighter on the dash,  both batteries charge simulaneously.
If I want to recharge only the Aux battery I plug the solar panel into a
second lighter socket I had installed behind the driver's seat.  It is very
flexible.  Radio Shack has many of the smaller components, pigtail
connectors, etc.
    To accomplish this, you must "isolate" one battery from the other.
Since this was done by my van's PO, I cannot comment
on this process.  This is a critical part of "house" battery use, for you do
not ever want to tap into the power of your starter power.
    My solar panel measures 11 x 19" & is approx 1/16" thick.
It can put out 8 watts of power while in full sun/good angle.
I have not yet tried using my new laptop with my system, but
will be soon.  So, don't know if 8 watts is adequate.  If it is not,
I will simply call Real Goods Trading Co & find out how many
more watts I need.  Solar panels come in a variety of wattages.
It is perfectly easy to use them in tandem--& can be more useful that way,
at times.  Just be sure & buy the "bulletproof" type.
Hope this helps,
Phaedra
'85 Westy-Wolf
"Hester"