I like the idea of a switched 3rd light for tail-gaters and/or high beamers. 

I got this for all those reasons, backing in strange, dark areas, tail-gaters, high-beamers:

http://www.gowesty.com/ec_view_details.php?id=23283&category_id=&category_parent_id=

Switched separately.

An additional by-the-way about installing a separate back up light: since I camp so much,
It is a necessary and helpful addition. And, since I've chosen to use a HID light, there is no
other installation than separate switch, by the nature of the HID. 

For people who don't camp, I can see where they might start fabricating imagined stories
about the possibilities and concerns of "leaving the light on".... but, as I've been camping
in my 3 different Vanagon's since '88, I've never backed into a camp spot, at night, when
the light was needed, then left it on while I exited the vehicle, gotten inside the van via the
side slider, popped the top, then 3 days later driven off with the separately-switched back
up light on. Pretty dumb and sillly when looked at in a practical sense, innit. ;-)
Turning a HID on via that switch, takes about 30 seconds for it to "heat up" the gas to
reach full brightness, so that ONLY happens in camp spots, and is very easy to discern
that it is on, as it turns dark night into BRIGHT daylight.

I don't drive my vanagon "aggressively", so I don't use practices that would try to piss off
other drivers. I DO inform people when they are driving in a way that is dangerous or
distracting, such as with brights on, but then others do the same for me when I make the
mistake of leaving my brights on when they shouldn't be. Life is a spontaneous, rolling
journey, and there are many things I don't get to "vote" about, and a few I do. I try to be
thoughtful about the things I can control, and accommodating and adjustable for the
others. I might turn on that rear back-up light periodically, but I don't leave it on to
over-make a point with a driver behind me.
YMMV,
Bob