One thing to remember is that your solar gen will be highest when your
fridge needs it most, ie during the day and when the interior of your van
may be incredibly hot as well.

I have an indoor/outdoor temp gauge that in "warm" weather (80+) regularly
reads 120+ interior tempature due to the solar heating.  That'll pretty much
eliminate any hope of the fridge keeping itself cool during the day.  Note,
when I'm actually using the fridge I keep the windows open in hot weather to
keep the interior somewhat cooled down.

This all makes me want to get a solar powered roof vent/fan that'll fit in
the sun roof.  I don't like leaving the windows all wide open when I'm out
away from my van all day.  Invites all sorts of pest to fly or reach in...

There is no perfect solution.  Last week I was camped under the redwoods,
solar panels would have been useless... as would wind...  The only thing
that is 100% reliable is a minature generator...  yuk (personally).    IMHO
I would never count on batteries helping for more than 24 hours between
being charges...  If you want long term power, you need to generate it on an
as needed basis by something other than your engine.

-Jon