RE: Solar panels and Westy
A search of the WetWesties message arcives and the vanagon.com archives will
find a lot of discussion on this subject.
A brief summary:  You need the solar panel(s), wiring to a solar charge
controller of adequate size for the output of the panel.  That attaches to
the aux battery.  And that assumes that you have a second (auxiliary)
battery installed with the proper relay or separator wiring between the
starting battery and the aux battery so that the aux charges from the
alternator while the engine is running.
Some mount their solar panels to the pop top of their Westies while others
use free standing panels that can be set up away from the van in the best
place/angle to get maximum charging.
You will want to calculate your use of aux power to determine how much
charging capability you need to meet your requirements.