Mercury switches can be a bit fussy to find the right spot to mount; I played around with one in my 2dr about 30 years ago and eventually removed it. Other options are a pin switch, or a reed switch (and magnet).

This place sells some interesting lights:

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Ffestoon.html%23hp

I would recommend warm white if you use LEDs; the blue-white that you commonly see on bikes and cheap lights are crappy for distinguishing colors. One of the festoon bulbs with six of the SMD emitters (LEDs) will be plenty bright inside your trunk.

Bill