A variation of Martin's electrical connection:

So many electronic products today run off of a transformer which
converts AC to DC.

With Martin's IKEA light or some others, instead of hardwiring into the
van, could you just cut the wires near the transformer and attach a plug
to go into the cigarette lighter, called a power source in newer
vehicles?  Plugs like this, with or with out extra cords are available
at Radio Shack and elsewhere.   ( I stepped on the lighter plug to my
portable tire pump and replaced it with one that had an extra 36" of
cord from RS - make pumping the rears up much easier.)

My electronics knowledge is limited and rusty - so there may be
"obvious" reasons why this is a clear cut "no can do."  There may be
good reasons to install an inverter and then use the transformers that
come with the products.  But it seems unnecessary to change DC to AC and
then AC back to DC.

But I have just bought an 85 Westy Weekender with 10k miles on a rebuilt
engine and am thinking about improvements to enhance camping and traveling.

Sam Walters
Baltimore