I put the light right under the cross brace mainly because I wanted a good negative connection but it also served well as an attachment point. It is amazing how soft that metal is and how easy it is to drill into.

 

I bought one of these:
http://www.superbrightleds.com/specs/spotlight.html

Titanium seems to match the stock interior, IMO. The little red light it emits when it is charging looks cool in the dash as well. Bright light.