Thanks. I interpret that as a hinge at the front and a pair of hinge/latches to either side. That would be a very flexible set-up.
I was thinking of what you could do without a penetration through the roof. Instead of a LED light bar you could have a 'hood ride VW' style driving light;
http://www.pictaram.com/media/1206933857952304902_2150582274
...and a 110v outlet at the back. I've only experimented with PolyMetal, this was maybe $10 worth of scraps:
This was sheared, braked and rolled by hand, with an 18" lever arm. The nice thing is it's prefinished (I think it had a peel-off paper coating) so once it's shaped You're done.
What size would the four pieces be to en-blister the roof rack?