There are DOT approved outboard motor fuel containers that fit quite well
into the westy luggage tray.  They can be siphoned with out removing the
container into your fuel tank.  Tempco is the brand if I recall.  6 Gal
capacity.  West Marine sells them.   I've used one for many trips where
200mi was stretching it, especially offroad where one's fuel consumption is
often somewhat unpredictable.  There is a wealth of lore and information on
NATO fuel cans out there.  Just take a look.  These are valuable enough
that mine was stolen from the rear rack (yes it was locked on) from the
driveway  s It was an Australian DOT 20ltr in flaming red mounted higher
than the average vehicle impact point on a Gary Lee rack.  If you aren't
sleeping in the van, just put the can full or empty inside to be less
conspicuous to the rabble.

Treatise on Jerry cans here:
*http://tinyurl.com/jerrican*
Of course if you are sleeping in the van you may have to use your home
defense equipment to dissuade the home invasion theft of your
wedco/nato Jerry can.
 A plastic outboard motor fuel tank is much less tempting.

Visit the POR-15 site for a fuel can sealer kit.  Not cheap but cheaper
than a new NATO can.

Pensionerd