There is a company here in Sacramento making fuel cells.  They have a model
which is smaller than a battery [a little longer, but narrower and
shallower] which produces 1.8 kw.  Seems to me this would power a van's
electrical needs while camping without problems.  I think it runs on air and
bottled hydrogen, and because of the contaminants in the air [and maybe in
the H2 the cell has to be purged periodically.

I'm going to find out what's needed to install and run it.  Let me know if
you're interested.

Mike

PS:  While I have no financial interest in this company my daughter works
for them developing fuel cells so I'm not a completely disinterested party.