I'd love to have a solar panel, but every time I ran the numbers it
seemed like it wasn't really that good a deal, based on my pattern of
camping.     The issue I'm considering is Solar Panel vs. just more
battery capacity, vs. length of stay.

Let's say you want to spend $250.

Solar Panels:  You can get a 50W solar panel w/controller.
   This will give you 300WH/day (assuming 6 hours of good sun-
equivalent)

Batteries:  You can get 4 deep cycle 100AH batteries.
   This will give you 2000WH of capacity (assuming 50% draw to keep
the batteries happy)

Based on these numbers, it seems to me that you when you set up camp,
the solar panel system won't begin to be better until you've been
camping for around 6 days straight.

Solar Panel Issues:  The solar panels also need some attention (you
have to park in the sun if mounted on the van, or else set them up in
the sun.  Some worry about theft?  Cloudy days?

Battery Issues:   Weight & size inside the van.  Adding more lead to
the environment?   How long of a drive would it take to recharge them
fully?