The very best interior lighting upgrade I've got in my van is a bunch of
those LED headlamps.  I have the normal hard-wired lighting and a couple of
extra incandescent fixtures, too...but I have half a dozen or so of those
battery headlamp...3 AAA bats in a small case with leds on the front.....
with an adjustable elastic headband and a 'tilting' feature to raise and
lower the 'aim' of the beam.

 A couple even have a red LED only position to read maps without wrecking
your night vision...

 It's really handy to have light right directly where you look, with just a
touch of the button on your forehead....if you are bald like me, it's on
your 5-head...I just snag the nearest one and slip it on my head, walk
around the camp, work on the van, crawl in bed and read...whatever needs
light.  The batteries last about a month with daily extended usage and they
cost maybe $10-20 each...inexpensive and simple.  I have enough for everyone
around...because everyone always 'borrowed mine' when I had just one or
two....

  Don Hanson