The 4xUB12220 is a good setup.  Thanks to Karl Mullendore
of WestyVentures for identifying this setup.  See:
http://westyventures.com/parts.html
half-way down the page.  This gets 88 amp-hours of deep
cycle power.

This was beat to death last year and nobody could find a
setup with more amp-hours to fit under the driver seat.
If you want more, you have to go under the rear seat, or use
the storage compartment next to the AC outlet.  Kurt Long
of Seattle has that setup with 100 amp-hours or more in a
BIG battery.

Re: cigarette lighter sockets.  Mark Drillock identified
a classy, very well made socket and plug pair that can
twist-lock to stay in place.  Either I can go to my shop
and poke around to find the source, or you can search the
archives for Mark's post sometime in the August-October
time period as I recall.  Hmmmm...guess I'll let you do
the search.  ;-)

Richard